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Milwaukee Electric Tool Corp. v. Snap-on Inc.

United States District Court, E.D. Wisconsin

September 22, 2017



          J. P. Stadtmueller U.S. District Court

         This is a patent case about lithium-ion batteries used in power tools. Before the Court are the parties' claim construction briefs and their cross-motions for summary judgment. For the reasons stated below, the Court adopts Plaintiffs' proposed claim construction in all respects. The Court further finds that Snap-On has not proffered sufficient undisputed facts to warrant summary judgment on the grounds of derivation or pre-suit damages. Likewise, Plaintiffs have not shown that the undisputed facts support application of assignor estoppel against Snap-On, although IPR estoppel does operate to bar some uses of some of Snap-On's prior art references. Finally, the Court determines that there is an insufficient factual basis for Snap-On's claim of invalidity, its inequitable conduct defense, and certain aspects of its anticipation defense, and so these will not be permitted to proceed to trial.

         1. BACKGROUND

         Plaintiffs assert infringement of the following claims against Snap-on: claims 1 and 8-10 of U.S. Patent No. 7, 554, 290 (the “‘290 Patent”), claims 1, 4, 5, 7-13, and 16-19 of U.S. Patent No. 7, 999, 510 (the “‘510 Patent”), and claims 1, 8-10, 12, and 13 of U.S. Patent No. 7, 944, 173 (the “‘173 Patent”). Independent claim 1 of the ‘290 Patent, which is representative of its counterparts, recites

a battery pack for power a hand held power tool, the battery pack comprising:
a housing connectable to and supportable by the hand held power tool; and
a plurality of battery cells supported by the housing, the battery cells being capable of producing an average discharge current greater than or equal to approximately 20 amps, the battery cells having a lithium-based chemistry.

(Docket #187-1 at 77). Further, later claims provide, in relevant part, that the pack's battery cells each have “a nominal voltage of 4.2 volts” and that they have “a capacity of approximately 3.0 ampere-hours [(“Ah”)].” Id.

         Because of the vast factual record presented, the Court will provide here a broad overview of the relevant background and timeline. Facts pertinent only to one narrow argument or another will be discussed at the appropriate juncture. This may lead to some repetition, but the Court has found no better way to fully and fairly treat each matter for decision.[1]

         Power-tool companies, including Plaintiff Milwaukee Electric Tool Corporation (“Milwaukee”), began manufacturing high-power cordless tools in the 1980s, and those power tools were traditionally powered by nickel-cadmium (“NiCd”) or nickel-metal hydride (“NiMH”) battery cells contained in battery packs. In the 1980s and 1990s, lithium-based battery technology emerged, and was initially used in low-power applications such as cell phones and laptop computers, later migrating to high-power applications such as electric automobiles and satellites.

         Canadian battery manufacturer E-One Moli Energy (Canada) Ltd. (“Moli”) was “a world leading manufacturer and researcher of lithium-ion (“Li-ion”) batteries, ” and had a “large and accomplished world class team” that took on “pioneering roles in the advancement of lithium-ion technology.” (Docket #187-26 at 8-9). Like other battery makers, Moli initially focused on low-power applications, but by the early 2000s it was focused on high-power uses, including power tools, for which it developed battery cells.

         In June 2001, Mark Reid (“Reid”), a Moli employee, prepared a presentation for toolmaker Bosch called the “Bosch 24V Power Tools Presentation.” In the presentation, Reid showcased Moli's Li-ion battery packs. Two videos embedded in the presentation show a Moli employee using a Bosch reciprocating saw retrofitted with Moli Li-ion cells cutting steel pipe and wood. The presentation goes on to describe the benefits of replacing NiCd battery cells with Li-ion ones, including increased power, reduced weight, and longer shelf life. The presentation also depicted common NiCd battery pack features, including a housing, connectability of the pack to the tool, and a locking assembly.

         On July 25, 2001, a sales representative of Moli wrote to Milwaukee, attaching a modified version of the Bosch presentation, as well as a “Power 2000” presentation created by Moli scientist Ulrich von Sacken (“von Sacken”), which described Moli's Li-ion cells and promoted their ability to provide cost-effective power for high-power applications. Moli's sales representative also visited the company in July 2001 to introduce Milwaukee to the Moli cells.

         A month later, on August 27, 2001, Milwaukee product manager David Selby (“Selby”) met with a Moli representative. In an email to his colleagues the next day, he said that during the meeting he heard “disturbing news.” (Docket #187-33 at 2). Moli had apparently reported to him that it was working with other power tool manufacturers to develop Li-ion battery packs. Id. He said that Milwaukee nevertheless wanted to evaluate sample packs, and he set up a second meeting for September 18, 2001.

         Moli provided two sample battery packs on September 24, 2001. Jan Reimers (“Reimers”), a Moli scientist, stated that the packs' designated discharge currents, such as “20A”-meaning “20 amps”-denoted “the maximum current that the cell can be discharged at and still return >70% of the rated capacity.” (Docket #187-3 at 2). The battery packs sent in September 2001 were designated 15A.

         At this point, it is helpful to foreshadow one of the forthcoming claim construction disputes. As noted above, independent claim 1 of the '290 Patent and independent claims 1, 9, 10, 12, 16, and 18 of the '510 Patent recite “the battery cells being capable of producing an average discharge current greater than or equal to approximately 20 amps.” This is known as the “20 Amp Limitation.”[2] Much of the parties' disagreement regarding construction of the 20 Amp Limitation revolves around how to test it-in particular, how to measure the “average discharge current” of a battery pack. The facts regarding cell testing and development, discussed further below, will feature prominently in resolving that and other disputes.

         As noted above, Moli created two prototype packs, each comprised of a housing and a plurality of five Li-ion 15A cells connected in series. One of the named inventors of the patents-in-suit, Gary Meyer (“Meyer”), a Milwaukee employee, tested the prototype packs during the period of September 26 through October 11, 2001. First, he used a constant-current discharge test, in which the pack was configured to discharge at a constant current of 20 amps to see if it could provide this current over its entire capacity without failing. Moli's prototype packs failed this test, as they were able to deliver 20 amps only for a short time, delivering just a fraction of their entire rated capacity of 3.0 Ah before experiencing voltage crash, ending the test. (Docket #201 ¶ 41).

         Meyer also performed a cutting test, in which he attached a prototype pack to a circular saw and made cuts through wood. The prototype pack was observed to produce an average discharge current of 26.19 amps. However, the results showed that the actual performance of the pack ranged from over 50 amps to near zero during the course of the test. The pack was able to power the circular saw to make 34-37 cuts. Nevertheless, Meyer saw the test as a failure and concluded that the prototype pack was “unsuitable for use with a power tool requiring high discharge currents” because “the temperature of the Pack rapidly increased above acceptable levels” and the voltage of the pack fell below acceptable levels during the cuts. (Docket #187-17 at 74-75). Indeed, as Meyer saw it, the test essentially destroyed the pack. (Docket #201 ¶¶ 36-37).

         In addition, Meyer performed a pulsed current discharge test. During that test, the prototypes were able to deliver at least one period of constant-current discharge of 20 amps of a little over three minutes. The packs were still not able to deliver that current for their entire rated capacity.

         As it will be important later in considering Snap-On's inequitable conduct defense, it should be noted here that in 2009, during the prosecution of the ‘290 Patent, Plaintiffs disclosed the test results of this initial testing of the prototype packs. The results were submitted as an attachment to a declaration Meyer submitted to the United States Patent and Trademark Office (“PTO”). The PTO considered these results before granting the patent. In fact, the examiner first mistakenly believed the test results from the prototype packs were results of Plaintiffs' testing of the claimed packs and rejected the application on the basis that the results showed an inoperative and unsafe invention. When Plaintiffs informed the examiner that the prototype packs were not theirs but were the early Moli prototypes, the examiner reversed his decision and granted the ‘290 Patent.

         On October 16, 2001, Moli sent several more presentations to Milwaukee promoting the advantages of their Li-ion batteries over existing chemistries. Next, Meyer performed another cutting test on the prototype packs on October 17, 2001. During this test, Meyer made concurrent cuts into a board without shutting the saw off between cuts. The pack was able to make a little more than half the total number of cuts before it overheated and stopped. He allowed the pack to cool and finish making his cuts. In total, the pack powered 70 cuts.

         Again, as will be later relevant, Meyer did not mention this test in his 2009 declaration to the PTO. Plaintiffs explain that the test was not disclosed because there were no formal test results compiled from it. Moreover, Plaintiffs contend that this test, like the first cutting test, was a failure because it destroyed the pack in the process. However, Meyer did report this test to Moli employee Blair Tweten (“Tweten”), in response to Tweten's email trying to set up an additional meeting. Tweten explained that Moli could offer “insite [sic] into cell chemistry and potential changes [they] may be able to offer.” (Docket #187-18 at 3). Meyer responded in an excited tone that he was able to use the prototype pack to make 70 cuts with a circular saw, although he was forced to give it a break in the middle because it overheated.

         That same day, Meyer informed Selby, among others, that he had done some “quick tests” on the Moli cells and found that they “did much better than their published specification sheet [and] ran some of our tools OK.” (Docket #209-54 at 2). While he expressed that there were “[s]till issues of cycle life, safety, etc., ” he concluded that the cells were promising enough that it was “definitely worth doing some further investigation.” Id.

         On October 23, 2001, Milwaukee employees traveled to Canada to tour Moli's facility and to discuss working together. Milwaukee's presentation during the meeting appears to describe the various packs it produced, as well as those of competitors. See (Docket #187-37). On October 29, 2001, Selby sent an email to Meyer and Jeffrey Zeiler (“Zeiler”), another of the named inventors, attaching a forecast of sales of Li-ion battery packs. (Only the email, and not the forecast, appears to have been provided in the record.) On October 30, 2001, Zeiler emailed Tweten indicating that Milwaukee was sending Moli two driver-drill kits to give Moli “the opportunity to play with them and get a feel for the power required to run them.” (Docket #187-39 at 2).

         On November 1, 2001, von Sacken sent an email to Meyer and Zeiler in which he suggested that Moli provide higher power cells in the form of packs with three parallel high power 18650 cells, with a total capacity of 3 Ah, in place of the 15A-26650 cells, since, in von Sacken's opinion, Milwaukee seemed to want to use the cells in the circular saw “and other power hungry applications.” (Docket #209-22 at 2). Moli provided a pack of 18650 cells to Milwaukee on December 17, 2001, in which five cells were placed in series with three strings in parallel.

         On November 26, 2001, Reimers sent an email to Meyer and Zeiler enclosing a report that detailed certain trade-offs between cells optimized for high energy (the 15A cells included in the prototype packs) and those optimized for high power (25A and higher cells), including “1) some typical spinel cycle life data, 2) more information on the capacity/cycle-life trades offs [sic], and 3) some low voltage recovery data.” (Docket #187-40).[3] In this report, Reimers discusses various Li-ion cells that could be made for Milwaukee battery packs, including 15A-26650-R1, 25A-26650-R1, and 40A-26650-R1 cells.

         On November 27, 2001, Reimers sent an email to Milwaukee following up on a November 15 conference call. In the email, Reimers confirmed that the battery cells in the prototype packs had been 15A cells. Reimers also reiterated that Moli had more powerful cells. He stated that he had sent Milwaukee 25A cells (which Snap-On says Moli had previously designed), would send additional cells in December, and was working to finish development of 40A cells.

         Plaintiffs disagree with Snap-On's implicit contention that Moli had higher amperage cells in the works from the start. They posit that it was Milwaukee that had affirmatively asked about whether higher power cells were available. However, von Sacken averred that the 25A cells could be easily produced but were not provided initially as Moli could not at that time manufacture them on a large scale. After Milwaukee's request, Moli assembled and provided 25A cells.

         Milwaukee received the 25A cells from Moli by December 6, 2001. Project meeting minutes note that Moli had changed the chemistry for the 25A cell from the 15A cell. The improvements were Moli's idea, although Plaintiffs nevertheless maintain that the 25A cell was not assembled until they asked for it. See (Docket #213 ¶¶ 9-10).

         In January and February of 2002, Moli made further changes to its cells, including an electrolyte change, which enabled it to create a 30A cell capable of performing better under a load. During this time, Moli projected that a 30A cell could be delivered in early March 2002. By mid-April 2002, Moli sent more than 20 battery packs equipped with Moli 30A cells to Milwaukee.

         Milwaukee tested the 25A and 30A cells in April and May 2002. These tests included tests at various currents and under various conditions, but among the current levels were 20 amp tests. Milwaukee test data dated May 14, 2002 shows the 25A and 30A cells performing a 20A constant-current discharge test while maintaining capacity of 2.58 and 2.75 Ah, respectively, over the entire discharge. Other test data shows a pack of 25A cells was able to maintain a 2.90 Ah capacity over the entire discharge.

         On May 2, 2002, Milwaukee employee Robert Disch (“Disch”) calculated the 3A constant-current discharge capacity for the 25A-26650 cell as 2.61 Ah. He found the cell had a calculated capacity of 2.58 Ah in the 20A constant-current test. Disch also calculated the 3A constant-current discharge capacity for the 30A-26650 cell as 2.79 Ah. He found the same cell had a calculated capacity of 2.75 Ah when subjected to the 20A constant-current discharge. He sent his results to Meyer that day.

         Zeiler updated the Milwaukee board of directors on the status of the Li-ion development project on June 26, 2002 through a PowerPoint presentation. In this update, Zeiler reported that the 30A Li-ion battery packs were outperforming existing Milwaukee NiCd packs by over 40 percent, as shown in screwing, drilling, and cutting tests. The presentation further explained that when the 30A cells were placed under heavy continuous discharge-e.g., 30-40 amp saw cutting-Milwaukee found that the temperature of the packs would sometimes rise to unsafe levels. To combat this, Reimers suggested adjusting the cell chemistry and electrode size by creating a longer, thinner electrode and improved electrolyte. The presentation also stated that one problem was that the “[c]ells need to change from 65mm length to 70mm to maintain 3.0Ah capacity.” (Docket #187-47 at 10).

         On August 16, 2002, Moli sent 40A cells to Milwaukee, and August 22, 2002 meeting minutes indicate that battery packs with the 40A cells were to be sent on September 1, 2002. On September 18, 2002, Meyer sent an email to the project team reporting testing data for the 40A-R3 cells. Among several tests, one showed that the 40A-R3 cell could deliver 96% of its rated capacity when discharged at 20 amps and nearly 89% of its rated capacity when discharged at 30 amps. On October 1, 2002, Meyer emailed the project team reporting additional test data for the 40A-R2 cells, which showed the 40A-R2 cells were capable of delivering approximately 94% of their rated capacity when discharged at 20 amps. The next day, on October 2, 2002, Reimers emailed the project team confirming that Moli was attaining similar test results.

         Plaintiffs state that conception of their invention occurred on or about November 21, 2002. Milwaukee's contemporaneous documents shows a priority date for U.S. Application No. 10/721, 800 (“the '800 Application”), the parent application for the subject patents, of November 22, 2002. Plaintiffs explain that the November 21 date was chosen because that was the day the inventors prepared an invention disclosure document. Plaintiffs contend that they actually reduced to practice the invention no later than December 12, 2002. That day, there was a project meeting between Milwaukee and Moli. During the meeting, Reimers reported the preliminary testing results of the new, longer 40A-26700 cells. This testing showed these longer 40A cells delivered approximately 95% of their rated capacity when discharged at 20 amps. The data from these tests is reflected in the minutes for a January 9, 2003 project meeting. At that meeting, Moli reported that the longer 40A cells would be ready to be placed in battery packs by January 13, 2003. Moli also reported that it had sent three such cells to Meyer by the date of the meeting.


         Claim construction requires the Court to determine the meaning and scope of the disputed claim terms. Markman v. Westview Instruments, Inc., 517 U.S. 370, 384 (1996). The interpretation of patent claims is a question of law for the Court. Id.

         To construe a given claim, “the court should look first to the intrinsic evidence of record, i.e., the patent itself, including the claims, the specification and, if in evidence, the prosecution history.” Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 (Fed. Cir. 1996) First in importance is the language of the claim itself as allowed by the examiner. Bell Commc'ns Research, Inc. v. Vitalink Commc'ns Corp., 55 F.3d 615, 619 (Fed. Cir. 1995).

         The words of a claim are generally given their ordinary and customary meaning, which is “the meaning that the term would have to a person of ordinary skill in the art in question at the time of the invention.” Phillips v. AWH Corp., 415 F.3d 1303, 1312-13 (Fed. Cir. 2005) (en banc). Tethering construction to a person of ordinary skill in the art is critical, teaches the Federal Circuit, because such a person reads the words of the claims against the context of their meaning in the relevant field of study, including any special meanings or usages, and in light of closely related documents such as the specification and the prosecution history. Id. at 1313. Because of the sometimes specialized meanings attributed to terms based on the field in question, general-purpose dictionaries are not always useful. See Id. Before resorting to such a resource, courts should begin with the materials that a person of skill in the art would use: “the words of the claims themselves, the remainder of the specification, the prosecution history, and extrinsic evidence concerning relevant scientific principles, the meaning of technical terms, and the state of the art.” Id.

         After evaluating the claim language itself, the Federal Circuit instructs that the specification “is the single best guide to the meaning of a disputed term.” Vitronics, 90 F.3d at 1582. Although the patent specification may not be used to rewrite the claim language, SuperGuide Corp. v. DirecTV Enters., Inc., 358 F.3d 870, 875 (Fed. Cir. 2004), the specification may be used to interpret what the patent holder meant by a word or phrase in the claim, E.I. du Pont de Nemours & Co. v. Phillips Petroleum Co., 849 F.2d 1430, 1433 (Fed. Cir. 1988).

         After considering the claim language and the specification, a court may consult the final piece of intrinsic evidence: the patent's prosecution history. Vitronics, 90 F.3d at 1582. “[S]tatements made during the prosecution of a patent may affect the scope of the invention.” Rexnord Corp. v. Laitram Corp., 274 F.3d 1336, 1343 (Fed. Cir. 2001). This is especially true if a particular interpretation of the claim was considered and specifically disclaimed during the prosecution of the patent. Warner-Jenkinson Co., Inc. v. Hilton Davis Chem. Co., 520 U.S. 17, 30 (1997); Vitronics, 90 F.3d at 1582- 83.

         Generally, the body of intrinsic evidence will eliminate any ambiguity in the claim terms, rendering unnecessary any reference to extrinsic evidence. Vitronics, 90 F.3d at 1583. Yet, if needed, a court may consider extrinsic evidence, which “consists of all evidence external to the patent and prosecution history, including expert and inventor testimony, dictionaries, and learned treatises.” Phillips, 415 F.3d at 1317-19. Extrinsic evidence may assist the court in understanding the underlying technology, the meaning of terms to one skilled in the art, and how the invention works, but it may not be used in derogation of the intrinsic evidence. Id.

         2.1 The 20 Amp Limitation

         The heart of the parties' dispute in this case is the interpretation of the 20 Amp Limitation. This limitation reads: “the battery cells being capable of producing an average discharge current greater than or equal to approximately 20 amps.” The parties' competing constructions are:

Plaintiffs' Proposed Construction

Defendant's Proposed Construction

“the battery cells, when configured together in a battery pack, are capable of producing reasonably close to 20 amps of discharge current or greater over the course of delivering their entire rated capacity”

This claim term is indefinite under 35 U.S.C. § 112, ¶ 2. In the alternative, “battery cells capable of producing an average battery pack discharge current greater than or equal to approximately 20 amps when used with a hand-held power tool over a time period consistent with the intended use of the tool.”

         The parties' dispute, reduced to its essence, is quite straightforward: does this limitation require the battery pack to continuously produce 20 amps or greater of discharge current over its entire rated capacity, or must it merely be capable of producing an average discharge current of 20 amps or greater over its entire capacity?

         The Court's interpretive task is somewhat eased, as it is not writing on a clean slate. Another branch of this Court, Magistrate Judge William Callahan, construed this very limitation contained in the same patents in 2012. Milwaukee Elec. Tool Corp. v. Hitachi Koki Co., Ltd., No. 09-C-948, 2012 WL 10161527, at *3-4 (E.D. Wis. Dec. 11, 2012). Further, the Patent Trial and Appeal Board (“PTAB”) construed this limitation during inter partes review (explained further below, see infra Part 3.2.2). (Docket #179-11 at 9-11); (Docket #179-12 at 7-8). Every adjudicative body that has assessed the 20 Amp Limitation has agreed with Plaintiffs' proposed construction. Although this Court is not bound by those prior decisions, see Jackson Jordan, Inc. v. Plasser Am. Corp., 747 F.2d 1567, 1574 (Fed. Cir. 1984); Memory Integrity, LLC v. Intel Corp., Case No. 3:15-cv-00262-SI, 2016 WL 1122718, at *19 (D. Or. Mar. 22, 2016), they are persuasive, and this Court reaches the same conclusion for largely the same reasons, Markman, 517 U.S. at 390-91 (1996) (observing that courts can achieve consistent claim construction “through the application of stare decisis”); Key Pharm. v. Hercon Labs. Corp., 161 F.3d 709, 716 (Fed. Cir. 1998); Evolutionary Intelligence, LLC v. Sprint Nextel Corp., Case No. C-13-04513, 2014 WL 4802426, at *4 (N.D. Cal. Sept. 26, 2014) (noting that IPR proceedings constitute part of the prosecution history).

         First, the language of the limitation is not limited to any particular application or tool, contrary to Snap-On's proposed construction. Nothing in the claim language qualifies the limitation to discharge over a “non-trivial period of time, ” as Snap-On proposes. Hitachi, 2012 WL 10161527, at *4. Thus, the import of such language is that a pack satisfying this limitation must be “capable of producing the required level of current at any point, in any operation, with any high current hand held power tool.” (Docket #178 at 11).

         The specification, the next-best source of information for purposes of construction, corroborates this view. The patents-in-suit share a common specification: “the battery pack 30 can supply an average discharge current that is equal to or greater than approximately 20 A, and can have an ampere-hour capacity of approximately 3 A-h.” (Docket #187-1 at 76). The specification states that “the battery pack 30 can supply power to various power tools, such as, a driver drill 300, a circular saw 305, and the like.” Id. It can “power various power tools (including a driver drill 300 and a circular saw 305) having high discharge current rates.” Id. The specification states that the average discharge current associated with these exemplary uses should be 20 amps or greater. Thus, the specification contemplates many different applications and contexts for the battery pack in question, which is incongruent with Snap-On's suggestion that some specified tool, under some specified time interval, be used as the sole benchmark.

         As will be explained further below, because the skilled artisan would know that the constant-current test is the method for measuring conformity with the 20 Amp Limitation, Plaintiffs are not conjuring the phrases “reasonably close” and “entire rated capacity” from thin air, although Snap-On correctly notes that those terms are not found anywhere in the intrinsic record. Instead, Plaintiffs are simply reading the limitation in the way that it must be read; that is, with the standard explanation for how to measure it. The constant current test, as mentioned above, involves discharging the pack at a constant current and measuring how long it can sustain that current.[4]

         In addition to the claim language and specification, the prosecution history makes clear the distinction that Plaintiffs hope to draw between the Moli pack and theirs. The initial Moli prototype cells could discharge 20 amps in some applications, some of the time, but this was not enough. Indeed, it speaks volumes that the examiner, initially mistaking Moli's packs as Plaintiffs', rejected them. In so doing, the examiner stated: “Per one of the inventors, Gary Meyer, filed declaration under 37 CFR 1.132, it seems the claimed battery pack is incapable of delivery a useful average discharge current of 20 amps or greater.” (Docket #209-63 at 4). The examiner also stated that because the prototype pack only had 5 lithium-ion cells instead of the claimed 7-cells pack, there was “no convincing evidence that more than 5 cells would make the power tool operates [sic] in a useful and safe manner.” Id. Once the examiner's misapprehension was corrected, he allowed the claims to issue.

         Snap-On asks the Court to engraft an additional limitation onto the 20 Amp Limitation out of practicality-that is, because tools in the field are not routinely turned on and their batteries run down completely without pause. See (Docket #201 ¶¶ 5, 12-13). Snap-On reasons that “the word ‘average' in the 20 Amp Limitation implies that the discharge current may drop well below 20 amps so long as the average current remains above 20 amps.” (Docket #207 ¶ 127). According to Snap-On, it is unlikely that any power too would have to deliver a constant current discharge reasonably close to 20 amps for its entire rated capacity in any real-life application. (Docket #201 ¶ 12).

         But the standard of review is not what a person of skill in the art would find realistic; it is instead what a person of skill in the art would understand. There is no question that, putting aside matters of practicality, a person of ordinary skill in the art would comprehend the meaning of the 20 Amp Limitation, including the requirement that 20 amps be continuously delivered during the entire rated capacity of the battery pack. Such a person would understand that the limitation describes the capability, not the potential real-world use, of the invention. See Hitachi, 2012 WL 10161527, at *4 (“[T]he fact remains that the capacity of a battery is normally measured by discharging at a constant current until the battery has reached its terminal voltage, consistent with Metco's construction.”). This is true notwithstanding the fact that even Plaintiffs concede that tool simulations are an important part of assessing the real-world functionality of the ultimate product.[5]

         Finally, the Court rejects Snap-On's suggestion that the 20 Amp Limitation is indefinite and therefore invalid. A patent must “conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as [the] invention” 35 U.S.C. § 112, ¶ 2 (emphasis added).[6] If, when “read in light of the specification delineating the patent, and the prosecution history, [a patent claim] fail[s] to inform, with reasonable certainty, those skilled in the art about the scope of the invention, ” the claim is invalid as indefinite under Section 112. Nautilus, Inc. v. Biosig Instrums., Inc., 134 S.Ct. 2120, 2124 (2014). A claim “must be precise enough to afford clear notice of what is claimed, thereby appris[ing] the public of what is still open to them.” Id. at 2129; see also Interval Licensing LLC v. AOL, Inc., 766 F.3d 1364, 1370 (Fed. Cir. 2014). Moreover, a reviewing court must remember that “[i]t cannot be sufficient that a court can ascribe some meaning to a patent's claim; the definiteness inquiry trains on the understanding of a skilled artisan at the time of the patent application, not that of a court viewing matters post hoc.” Nautilus, 134 S.Ct. at 2130.

         A claim is indefinite where it can be measured in several ways and the claim language, considered against the specification and prosecution history, do not provide adequate guidance on which method to use. See Teva Pharms. USA, Inc. v. Sandoz, Inc., 789 F.3d 1335, 1344-45 (Fed. Cir. 2015); Eli Lilly, 845 F.3d at 1370. Put differently, “the patent and prosecution history must disclose a single known approach or establish that, where multiple known approaches exist, a person having ordinary skill in the art would know which approach to select.” Dow Chem. Co. v. Nova Chems. Corp., 803 F.3d 620, 634-35 (Fed. Cir. 2015).

         However, “a patentee need not define his invention with mathematical precision.” Invitrogen Corp. v. Biocrest Mfg., L.P., 424 F.3d 1374, 1384 (Fed. Cir. 2005). Instead, “[t]he definiteness requirement mandates clarity, while recognizing that absolute precision is unattainable.” Apple Inc. v. Samsung Elecs., Co., 786 F.3d 983, 1002-03 (Fed. Cir. 2015) (quotations and alterations omitted), rev'd on other grounds in 137 S.Ct. 429 (2016); Nautilus, 134 S.Ct. at 2128 (recognizing that “[s]ome modicum of uncertainty” may be tolerated). Indefiniteness is a question of law and must, like any other invalidity defense, be proven by clear and convincing evidence. Sonix Tech. Co., Ltd. v. Publ'ns Int'l, Ltd., 844 F.3d 1370, 1377 (Fed. Cir. 2017); Teva, 789 F.3d at 1345.

         Snap-On's indefiniteness objection has two aspects. First, it says that Plaintiffs conveniently used functional language-the requirement for a 20-amp discharge current-just at the point of novelty from prior art, which is not permitted under General Electric Co. v. Wabash Co., 304 U.S. 364, 371 (1938). However, the Federal Circuit has explained that functional language, standing alone, is not sufficient to render a claim indefinite. Application of Swinehart, 439 F.2d 210, 213 (C.C.P.A. 1971); Cox Commc'ns, Inc. v. Sprint Commc'n Co. LP, 838 F.3d 1224, 1232 (Fed. Cir. 2016). Although neither expressly considered the matter, is it worth noting that neither Magistrate Callahan nor the PTAB had difficulty in construing the 20 Amp Limitation, much less such insurmountable difficulty as to render the limitation indefinite. Rather, the relevant materials provide a skilled artisan with sufficient information to describe the claimed subject matter and distinguish it from prior art, which is all that is required. See Microprocessor Enhancement Corp. v. Tex. Instruments Inc., 520 F.3d 1367, 1375 (Fed. Cir. 2008). Snap-On devotes little space to this argument and does no more than point out the functional language, expecting that effort to carry the day, and so the Court need not address the point further. See Hardrick v. City of Bolingbrook, 522 F.3d 758, 762 (7th Cir. 2008); United States v. Berkowitz, 927 F.2d 1376, 1384 (7th Cir. 1991).

         The second aspect of the indefiniteness challenge is more involved. According to Snap-On, the 20 Amp Limitation is fraught with uncertainty as to how to test the “average discharge current” of the battery pack which a person of ordinary skill in the art could not unravel, including in relation to “how long the battery is used, the application or task for which the tool is used, the acceptable voltage performance, and even the ambient temperature.” (Docket #182 at 7). Put simply, Snap-On claims that a pack might not be able to produce a constant 20-amp discharge current over its entire rated capacity but could do so on average if used intermittently. (Docket #187-5 ¶ 32). In light of this, one of its experts, Yet-Ming Chiang (“Chiang”), opines that a pack must be tested in various ways that simulate real-world applications. Id. ¶ 34. This makes Meyer's 2001 cutting test and pulse test at least as relevant-indeed more so-that the constant-current test he performed. Id. ¶ 39; see also (Docket #187-13 163:6-23) (Reimers testifying that average discharge current denotes averaging the discharge produced during pulse or profile tests). On this point, Snap-On asserts that Magistrate Callahan failed to consider the issue of indefiniteness as reinvented by the Supreme Court in Nautilus, rendering his opinion less persuasive. See Dow, 803 F.3d at 630 (“[T]here can be no serious question that Nautilus changed the law of indefiniteness.”).

         Plaintiffs admit that tool simulation profiles are among the tests used to assess the performance of Li-ion battery packs. (Docket #201 ¶¶ 14-15). Moreover, other witnesses, include two of the named inventors, testified that a battery pack could be run both intermittently and constantly to ascertain an average discharge current. See Id. ¶¶ 24-26. Because of the diversity of potential testing conditions and applications, Chiang concludes that skilled artisans could reasonably differ in how they assess whether the 20 Amp Limitation is met and that the patents-in-suit, even when considered alongside the specification and prosecution history, do not provide adequate instruction on which test should be used. (Docket #187-5 ¶¶ 45-47); see also (Docket #187-10 47:19-48:18) (testimony of Plaintiffs' expert during IPR, opining that continuously running a power tool until its battery runs out is not a “typical” way such tools are operated).

         The Court does not agree. The Federal Circuit has found indefinite patent claims that do not teach how they are to be measured. For instance, in Teva, a patent claim prescribed a particular “molecular weight” of a product but did not specify which of three methods should be used to measure it. Teva, 789 F.3d at 1345. Neither the claims nor the specification provided guidance, and the prosecution history contained inconsistent statements by the patentee about which measure was correct. Id. at 1344- 45.

         Likewise, in Dow, the court considered a claim that required calculation of the “slope of strain hardening coefficient.” Dow, 803 F.3d at 631. The claim did not specify at which of several possible ways the “slope” should be calculated. Id. at 632-33. The Court of Appeals found that a skilled artisan would not be able to choose among them even after review of the specification and prosecution history, and so the claim was indefinite. Id. at 634. In so doing, it rejected the testimony of the plaintiff's expert that an artisan would know to select his method, since the expert's method “was not even an established method but rather one developed for this particular case.” Id. at 635.

         The situation here is different. As explained above, the claim language, considered alongside the specification and prosecution history, all indicate that the 20-amp discharge current must be constant throughout the rated capacity of the battery, regardless of application. This is determined by application of the constant-current discharge test, which the evidence submitted by Plaintiffs establishes as an industry-standard test. It is not, as was the case in Dow, an ad hoc test among other defensible methods of measurement.

         Plaintiffs offer a robust body of testimony to support the proposition that the constant-current test is the proper way to measure the 20 Amp Limitation. First, their expert, Ehsani, opined that a skilled artisan would understand that the 20 Amp Limitation referred to the capability of a battery pack under constant current discharge, not during a real-world application. (Docket #191-71 ¶ 23).

         Next is Zeiler, who testified that the constant current discharge was “the industry standard and the de facto measuring stick we used to determine whether a cell at that time. . .was capable of performing in a real world application.” (Docket #179-27 53:17-22). He explained that the “20 amp constant current discharge at the time was the test that was the bare minimum a cell needed to do to be able to build the confidence for any technical team to understand whether or not it could actually work in the field.” Id. 53:25-54:4; see also Id. 57:19-22 (to be successful, the cell at a “minimum had to be able to deliver a 20 amp constant current discharge”). Zeiler testified that 20 amps represented the low end of operational power for a power tool, while the high end was somewhere around 80 amps. (Docket #172 ¶ 128).

         Similarly, Meyer claimed that he performed constant current discharge testing on the Moli packs in 2001 because such tests “were and are commonly used by power tool manufacturers to assess the suitability of a battery product for powering a tool.” (Docket #179-29 ¶ 6). Snap-On notes that Meyer admitted that a battery pack can be tested by other methods, including averaging the discharge current over a given time interval, but Meyer also opined that he would “normally” use a constant-current test. (Docket #187-14 159:3-160:19); see also (Docket #203-62 at 5) (from Handbook of Batteries, author David Linden notes that the constant-current discharge test “is becoming more popular for battery-powered applications”). Indeed, even von Sacken, Moli's former employee, testified that the constant-current test was “a very typical way of testing cells” because it made it “easy to measure capacity[.]” (Docket #203-49 65:18-66:25).

         Likewise, Selby testified that although the constant current test was one of “multiple ways” to test a battery pack, it was the “most typical” or “primary” test, and was used to cement “a basic first understanding or check of the battery pack's capability.” (Docket #179-32 32:9-33:4; id. 63:5- 64:7 (noting that the constant current test was “a standard criteria” in the industry); (Docket #179-34 ¶ 5) (averring that the constant current test was “a normal test procedure used by Milwaukee Tool”). Importantly, he opined that Meyer's other 2001 testing, such as the cutting test, was not a suitable method to determine whether the 20 Amp Limitation was met, as it was “not a controlled or any kind of scientific-type test.” (Docket #179-32 34:10-35:8).

         Snap-On points out that Meyer did not offer in his 2009 declaration about his 2001 testing an explanation of how the 20 Amp Limitation should be tested. Plaintiffs read Meyer's declaration to show that failure on the constant-current discharge test was sufficient to render the prototypes inadequate, while Snap-On asserts that the results of the other tests, including the cutting test, were indispensable to that ultimate conclusion. (Docket #201 ¶ 31). In Plaintiffs' view, the other tests merely assessed “certain characteristics” of ...

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