How not to kill a DeWalt flexvolt battery prematurely

One of my flexvolt battery packs died. Dissecting it, trying to re-use the cells. And figuring out why specifically just three cells at the bottom of the pack failed.

[@JeffGeerling]

Heh, I go online and buy the right security bit and wait a week for the bit to arrive, and then the battery sits for 6 months next to the unopened bit... Matthias defeats the security with a nail and a hammer and moves along with his day.

[@drescherjm]

Harbor freight sells the security bits for less than $10 for a wide collection of sizes.

[@JeffGeerling]

@@drescherjm you underestimate how lazy I can be! 😂

[@whirled_peas]

Small ones break easily but any bigger than T20 are basically impossible to snap, and difficult to drill

[@content4635]

Lol

[@Nono-hk3is]

Hi Jeff! BigClive would open it with a vise, a d sometimes a hammer (although he's usually more careful with battery packs)

[@quirlmaster9011]

There is nothing more Matthias Wandel then bandsawing a battery appart. I love it!

[@toolscientist]

Needs to make a bandsaw out of old batteries, then use that bandsaw to cut open a battery. That would be peak Matthias Wandel

[@georgedavall9449]

Man is amazing, I tell ya!

[@skatastic57]

me: I'll just buy the "security" torx bits to open it. Matthias: I'm gonna break it. Good job.

[@user2C47]

Me: Uses security torx as my only torx bits.

[@stanimir4197]

I like torx. Yet, torx size/design sort of suck, e.g you can use t15 bit in t20 head screw/bolt and it mostly works but with the tendency to round 'em off. Secure one mitigates that.

[@Anonymousee]

This deserves to be on the main channel. If others knew that they should throw all their batteries onto the charger periodically, it could save a lot of resources. I occasionally lost a battery in early spring (when work ramped back up) and didn't know why, but maybe that won't happen now that I will charge the full batteries before use.

[@thedave7760]

Also never run them down too low and if you can wait for 10-15 minutes to cool them off before charging them again. If you can, avoid fast charging that will help their lifespan as well.

[@matthiasrandomstuff2221]

it's not woodworking directly, and my battery related stuff is on this channel. It has a tenth the subs, but the views the videos get are the same, so which channel really doesn't matter in that regard.

[@charlesenfield2192]

I've encountered many different opinions regarding how charging affects battery life. I've always been "keep 'em charged" kind of guy. I usually run them until tool performance suffers rather than until they stop working. If they're not in use and below 50% I charge them, and if they're below 75% and I plan to use them hard I charge them first. Some people have told me that Li-ion batteries have a fixed number of charge cycles regardless of the depth of discharge, so if I charge one from 70% to full, I'm "wasting" a charge cycle and shortening the life of the battery. I would love to know if it's that's true or not. I suspect there's a kernel of truth to it, but like so much conventional wisdom on the internet, it's probably exaggerated or only partially true. For now I'm more concerned about excessive discharge than charging too often.

[@PaulSchaffert]

@@charlesenfield2192 You've got the right approach to making your batteries last. The charge life of a lithium battery isn't "wasted" for any given charge -70% to full is not equivalent to say 10% to full. There are charge profiles that reduce the lifespan of the battery - for example charging at 1C (charge current equal to battery Ah rating) is more stressful than charging at 0.5C and less stressful than charging at 2C. Many lithium ion batteries keep better when stored between 30%-70% charge while not in use, and avoiding a complete discharge may extend the life somewhat. Extreme temperatures when charging or in storage can also wreck batteries - keeping the batteries in a climate-controlled place will help more than micromanaging every charge event.

[@cooperised]

@@PaulSchaffert Except that lithium batteries don't like being kept fully charged. Modern phones have a "smart charge" feature which engages if you're charging overnight - it charges to 80% and then holds, only doing the last bit to 100% shortly before your alarm is scheduled - for exactly this reason. So regular charging is good, but charging to 100% is only good if you're going to use the tool fairly shortly afterwards. For longer periods without use the battery should be at mid charge ideally.

[@Kardall]

That's really interesting. I'll have to show this to my dad who has so many dewalt / cordless batteries that die... it's probably why they keep failing on him. He usually waits until he's down to one and it starts to not hold a charge for long (probably because of this issue) and then buys like a set with two batteries, then uses the batteries in all the things.

[@Fekillix]

I remember this being a big thing on the earliest Makita batteries (10 years ago). But then the issue was probably resolved, as I've never heard about it or dealt with a dead Makita battery since. I still have 8 year old Makita batteries in use.

[@brucelee3388]

It still happens. Thanks for reminding me that I need to put my batteries through a charger cycle.

[@jasonharrison25]

Yeah. First generation has a controller board the ran off one cell and if unused for several months would kill the whole thing buy locking out the charger. The trick to keeping them alive was to charge them every few weeks. I still have first generation ones that work from more than 10 years ago. The newer ones that have a star cast into the plastic case changed the design so the control board runs off the whole string of cells and has cell balancing. Still a good idea to keep them charged up at least once a month. And maybe even leaving them on the charger for a day or so so the cells can properly balance

[@apagg97]

Respect for that root cause analysis. I hope some Dewalt engineers are fans and realize.

[@MRrwmac]

Matthias, That is some very good Dewalt battery information! Glad you decided to figure it out! Hope you and your wonderful family have a great year in 2023.

[@aaronalquiza9680]

It's magical that you uploaded this video just as i was having a balance issue with one of my $300 battery packs from Milwaukee.

[@stoffel89]

Found your videos yesterday. Now im hooked. You explain stuff that even a kid can understand it. Keep it up.

[@iwayini]

Thanks for the video. I managed to replace a cell in a Makita battery which was much easier to dismantle and fix than Dewalt. I landed up building a spot welder as well which has come into into use quite frequently now for the battery packs.

[@Glipsnarp]

Have you tried building a portable battery bank or a car booster?

[@paulf1071]

Great investigative work to uncover the reason for the middle cells draining!

[@RiGGeN83]

thanks matthias for the information , i have 2 flex volt batteries that i hardly ever use, with this information you may have save my batteries and a lot more from other users.

[@ironhead65]

I had a 40V battery for my Ryobi brand lawn blower /weed whacker combo die, just like what you explained! I haden’t used it for a while. I checked the charge, 3 bars. So I used it normally (usually ~2 bars to complete the yard). Near the end of my work, it died and would no longer accept a charge! What you explained perfectly matches my experience.

[@fredriklinge]

Best advice for these batteries - thank you for investigating Matthias! I’ve had a barely used 12Ah FV battery die this way, and warranty is only 12 months.

[@georgesilverhawkstrailcame2297]

I agree completely. Very nice work here, this has been a very informative and educational video. With any lithium-ion cells (flashlights, headlamps, lanterns, power tools, power bank, etc.), I always put the batteries on the charger to top them off before using. I was just telling my son why he should do the same…. this conversation was just a week ago. I will share this video with him. Have a great day, George

[@juneritchie2498]

This is a real eye-opener, as they say, that will impact how I handle my batteries going forward. Thanks!!

[@MazeFrame]

That seems like a colossal oversight if it turns out the charge controller is in fact the the pack-killer.

[@matthiasrandomstuff2221]

Only if used infrequently. Probably not a regular use case for an expensive pack like that.

[@JeffGeerling]

​@@matthiasrandomstuff2221 For my own needs, I only have two of the giant flexvolt packs, and I use them exclusively for my mower. I use them every couple weeks during spring/summer/fall, but they sit all winter unused. I'll have to make sure to leave them a little discharged going into winter, and top them off before the first cut in the spring!

[@Orcinus24x5]

On the contrary, the engineers are more than likely aware and the bean-counters love it that way. More dead batteries = more battery sales.

[@whirled_peas]

@@Orcinus24x5 this is the most likely answer sadly. Every aspect of something like this is understood and engineered to the nth degree. Any flaws this fundamental are absolutely 100% deliberate.

[@JDeWittDIY]

@@JeffGeerling Leave them at 60% for over winter. Li-Ion cells don't like to be stored at 100% long term.

[@MyOwnUrl]

Awesome trick with the nail and hammer! You inspired me to open a couple dead battery packs I had lying around and the trick with the nail worked. Thanks for a great video as always. :)

[@PilchPlays]

Thank you for this. Was looking to design and 3D print an adapter for these batteries. Just hadn't dove into it yet to figure out what was needed to switch between 20V and 60V. I've made an adapter for the 20V Craftsman Batteries to power my TS100 soldering iron. Was looking to adapt the Dewalt batteries to make a bench top power supply from it.

[@JBALLMORE]

Very informative. I've heard so many say that batteries can go flat if you store them incorrectly. Now I at least know that I should charge my stored batteries before using them.

[@BillDavies-ej6ye]

Excellent diagnosis, Matthias, very helpful.

[@BA-zy2kb]

Awesome vid. It explains allot. I had 2 of 4 12Ah Flexvolts fail. One would not charge and the other has greatly reduced run time. Fortunately the first one failed within the 3yr warranty period and was replaced by DeWalt. I was going to try to swap cells to get one working unit but probably not after seeing the internal construction. Cheers!

[@Th3Pr0digalS0n]

Wow, thank you for this much needed information. You may have added years onto the life of my batteries.

[@cobaltyt19]

As always - a good source of electronics insight!

[@Friday0089-c7p]

Excellent info. I try to store all my batteries fully charged, but now I think I'll add a routine charging of I don't use them for awhile. Thanks for the info!

[@googacct]

The battery pack for the drill looks similar to the Milwaukee 12V batteries. I was able to extract the battery from the Milwaukee by using hot melt glue and a puller tab like is used in in paintless dent repair. Maybe something like a wooden dowel could be substituted for the pdr pull tab.

[@NormanRamsey]

Very cool. I love the engineering here. And the curiosity. Now I'm off to the shop to put my rarely used batteries on the charger.

[@Sqwince23]

When dealing with those start + Post security screws I typically find a straight bit screw driver and go between two points of the start and tangent to the middle post. tends to work the majority of the time and you don't have to bust out the pin in the middle.

[@jameshill4900]

Great video 👍 As a FYI both Princess Auto and Home Hardware sell a kit of security bits with all the types. Might be handy to have for a future teardown or repair.

[@howder1951]

Great info for us users Matthias, with battery packs like these so popular now, this is like an addendum to the user manual, thanks!

[@tomschmidt381]

Great analysis, I think you are correct as to the root cause of the failure. My drill and driver are 12V Bosch so they probably don't have an internal battery balancing circuit but I'll keep your findings in mind and periodically plug them into the charger.

[@StuartB_]

Very useful tip video Matthias, thanks. I don't use my flexvolt 9ah all that much so knowing not to run it all down at once before charging will save me £150 on a new one down the line.

[@ehRalph]

This is really good information, I have some yard tools that hit batteries hard, then they sit over winter. My batteries are compatible with some hand tools so I plan to rotate them in and easy use them + charge cycle a few times to balance things out.

[@Afraithe]

Wow, this makes so much sense. Ive had fairly good luck with my Dewalt batteries (as opposted to Husqvarna) for larger machines, chainsaw, mower, trimmer. But I will definetly remember this, charge them upp even if put away full.

[@plywoodcarjohnson5412]

This level of genius is beyond me. Congratulations!

[@JonnyDIY]

Cool, I'm sure Dewalt is aware of this "flaw" and loves it 🤣💕👍 Great vid as always

[@intelligenceservices]

Matthias, keep the springy clamps that connect the battery to the pins on the cordless tool battery mount. these little springy clamps can be put into a 3d printed adapter if you want to adapt one manufacturer's battery to a tool that it wasn't designed for. i've successfully done this with no problems with 20v tools of different manufacture. i didn't have any so i used springy paper binder clamp thingies and those also work, but it's much better to have the type that were made for the job.

[@kevinetheridge6153]

I found this to be a really informative video ( like most of them). Thanks, as always!

[@AWoodworkersLife]

That makes such good sense re. the third cell balance issue. Thanks Matthias.

[@SamsSweetAndSexyBBQ]

What a great video thanks for the info! I've also had a few Flexvolts die on me so far and that's great little tip for the future.

[@MikeCreuzer]

My understanding is that the bms is in the charger, not on battery and every tool has its own low voltage cutoff. An inspection of a 'normal' battery would show no bms on board. The flexvolt actually has a good amount of circuitry on top. There is both a mechanical and electrical interlock to get them to run at 15s 1p mode vs the default state of 5s 3p. The Dewalt and Bauer both expose each battery at the connector. For that external bms. I bought Dewalt expressly for this as I can use a hobby charger and balance charge and test and all the advanced features a hobby charger gives us. I love charging a flexvolt battery on my hobby charger at the lower voltage and using it in my chainsaw at the higher voltage. Solar powered chainsaw!

[@MikeCreuzer]

A single bad cell in this 3p configuration would pull down its two siblings as well. I seem to recall that the red shipping clip is called for during storage. It mechanically disconnects the battery from a 5s3p to three 5s1p. That would protect a single bad cell from becoming three bad cells. Until we try to use it.

[@MMSS12]

I have noticed too that few my makita batteries failed i looked inside and few cells started leaking and voltage was too low so i use the other cells in my flashlights. Great videos Matthias.

[@tweedeldee8122]

I love your videos and always learn something.

[@stevesas4744]

Like many people said in the comments below, you can usually charge up the low cells manually up to a level where the charger takes over and balances them all. But only do this on a relatively new battery which has been left discharged on the shelf for many months. Can be a faulty cell on older battery. I have recovered many like this.

[@stevebabiak6997]

Yes, if the voltage of an individual cell is close to but just under the threshold for charging, then that individual cell can be charged by itself, or the entire pack can be, but in either case it would have to be charged using something other than the factory charger.

[@Bob_Adkins]

@@stevebabiak6997 You just have to get that 1 cell up to about 3v with a hobby charger attached with clips or magnets and the factory charger will finish charging it.

[@stevebabiak6997]

@@Bob_Adkins - exactly, the factory battery charger for the entire battery pack won’t be able to do its job until that low cell is charged up using something else. And I didn’t bring into the picture that some tool battery manufacturers have a component in the battery pack that remembers a cell was low and keeps the pack disabled - I just can’t say that the brand being discussed here does that. But a brand that does that could leave the pack disabled even after the cells that were low were externally charged up to a proper minimum level.

[@Bob_Adkins]

@@stevebabiak6997 That's possible, but not very wise.

[@stevebabiak6997]

@@Bob_Adkins - there are brands out there that do that, and those who try to repair those battery packs have to bypass that “feature”.

[@maxspruit8370]

I bought a aliexpress spotwelder. It works very well with a big car battery as current supply ofcourse. Dont mean to spam you guys. This way breaking the spot welded taps is not an issue.

[@linsen8890]

Wow, this is really good to know. I have several DeWalt packs, some of which I don't use very often, but when I do use them, I run them down. I hope I haven't damaged them!

[@electrake2063]

I hate to say it now, but I’ve gotten years more use out of batteries like this by individually charging each cell one at a time, while in the pack, with a good lithium battery charger. Once they are all charged, you effectively reset all of them to an ‘equalized’ state, and they will tend to discharge evenly, and charge evenly. Oh, and never leave a pack below 50%, but also only charge to 100% when you really need it, I like the 75-90% charge level to gelt longer life out of my packs. I have some that are over 15 years old still working. By keeping it above 50% when stored you don’t allow any one cell to go below the min-threshold charge voltage, and the microcontroller doesn’t deem the pack unchargeable.

[@blzt3206]

Super interesting to me that I own a security torx bit set but you don’t as a former RIM engineer 😂 shows the skills you have - you don’t even need the right tool to get the job done. Nice work!

[@osvaldocristo]

Thank you, Mathias. That was exactly what I was looking for.

[@fjjfjfj]

Have had 2 36V Ryobi batteries die on me (under warranty) after completely draining them with the lawn mower. This is probably the exact same thing that’s happening with their batteries too! Thanks heaps Matthias!!

[@stevebabiak6997]

Hmmm, I thought that the BMS circuit board is supposed to prevent draining of the cells to a point below the low voltage limit. Good for you that the batteries were replaced under warranty.

[@fjjfjfj]

@@stevebabiak6997 this is what Matthias got into near the end with the dewalt batteries. They do but only halfway down the chain and only when charging. If they sit on the shelf for too long, some batteries may discharge faster than others and can cause them to break if you run the entire battery flat

[@JCLoony]

I have a 12Ah that died on me a while back, I think the failure mode was exactly like you described. I use these in my lawn mower, which takes 2, but does not use the 60V. I found that it usually empties one battery faster then the other, and I suspect that I had the now dead one on that side. I keep the still working ones on the charger all the time, so maybe that will help.

[@MCsCreations]

Yeah, it seems like a pretty bad BMS design in that pack. Weird. Stay safe there with your family, Matthias! 🖖😊

[@canoetipper019]

Happy New Year Matthias.

[@karlab9557]

Glad I watched to the end. That helps me know what to do. Thank you

[@MurCurieux]

This is exactly why I’m sub’d. Thank-you for the great videos.

[@Clark-Mills]

Yup, I just killed two of these packs doing exactly what you describe. :(. Thanks for the brilliant insight into why it happened.

[@positivemelon7578]

A good BMS should shut off if one of the cells is discharged too far (below 2.5V)...

[@matthiasrandomstuff2221]

the problem is that the tool is the one with the low volt shutoff, and it just sees the total voltage

[@glennextra]

I am pretty sure you are correct concerning the cause (and solution) I seen this being done in other products as well. If you had tried charging the 3 bad cells individually up to the voltage of the other cells, while still in the pack, you most likely could have recovered the pack and then could have put them on the charger for balancing. I have done this myself but on a 5 cell pack.

[@harenthiran]

How to charge the cell individually? What kind of charger can be used?

[@jayperez3431]

you have to inject low voltage with a probe on each cell until it gets to a detectable safe charging voltage for the dewalt charger@@harenthiran

[@dennispope8160]

I wonder if the regular 20v batteries have the same “problem” I’ve had a few “dead” dewalt batteries. Most the time I can “jump” them to another battery and get them up and running again sometimes I can’t. I had the same experience with trying to salvage the cells, they use some serious adhesive in the 20v packs I couldn’t get them apart.

[@MrHukd]

Some nice investigation there. Thank you👍

[@willierants5880]

This is a great video for a number of reasons. 1. Battery packs are outrageously expensive. 2. The more packs we save all the better for everyone and landfills except battery manufacturers.

[@actionjksn]

Harbor freight has a deluxe set of security bits and also you can often find a coupon for it. It comes in a reddish plastic box.

[@ObsessiveAboutCats]

This is very good info, thank you! I will make a point to do better about cycling my batteries.

[@emilee172]

If the cell is low and not shorted or open I have many times brought back cells with combination of slow/fast charges, they may not have the same potential as new but still work, many times a cell will get drained beyond its norm and now the charger does not see it, if you bring up that cell (s) voltage to about 2.75, it will again take a charge

[@jaycarneygiants]

The 1st 4:30 I thought this video was a waste of time... but at the 04:36 mark, it became constructive. Great video. Much appreciated. Thanks

[@francoisleveille409]

Would be awesome if you could check if this middle battery discharge is also true with the larger DCB612 and DCB615 packs.

[@CB-dx6hy]

Very useful information! Thank you.

[@damienkinchen]

I'm glad i watched this. I have 7 flexvolts thats been sitting up for well over a year. I need to balance them. 😵‍💫

[@MiscMitz]

Hmm. Never tried this with DeWalt but I have been successful with Milwaukee ones. Well, I've assisted my boss in repairing several. Side note, several higher end flash lights use those batteries, I saved a few for that purpose. And gave a couple to a friend who's vape uses them.

[@unperrier5998]

Much interesting video and investigation.

[@ib9rt]

"Don't run it all the way down" is probably good advice in general for preserving the life of batteries.

[@RGV2300]

actually, stated by dewalt in its website

[@Nono-hk3is]

It is for Li Ion batteries. But previous battery chemistries needed to be run down once in a while.

[@ib9rt]

@@Nono-hk3is Actually, not only for Li-ion batteries, it applies to nickel chemistry too. Where a battery has a number of cells in series, then running it all the way down is likely to reverse and damage at least one cell. For lead acid chemistry like car batteries it is even worse. Running a normal car battery even 50% down can damage it.

[@SinsBird]

@@Nono-hk3is Bs myth.

[@ockeojoj]

Thanks for this info, very useful!

[@typeaboutit]

And that is why you're my favorite KZbinr :)

[@stunimbus1543]

Wow what a brilliant video - I use Makita - don't know if they are the same, but going to follow the advice anyway.

[@hipjazzbone]

I love these videos. I just want to know how everything works. Once upon a time there wasn't much more than cells in these batteries. With the electronics on-board, is the charge controller inside the battery, or still in the charger?

[@fr33dumb0]

The one in his diagram is in the pack.

[@hernancoronel]

Hi Matthias, awesome investigation! How about designing a new matrix controller that would constantly rewire the batteries to prevent this from happening? Even simpler would be to modify the circuit to provide balanced charging and solve the issue much easier. Thanks for the video!

[@MikeKasprzak]

Good point, charging/balancing a battery before use, just in case the first cell has been sipped on for a long time

[@TopCat2021]

Very useful information thanks.

[@richardking6985]

I've had similar happen when I left a battery discharged too long. I hooked up a charger to the low cells then bring them back into range. Then top up each cell to balance out the pack. It revived a pack for another yr.

[@sloanNYC]

This makes sense, very good hypothesis!

[@Tugmun11]

Dude Thanks , Love your channel

[@FranciscoJavier32423]

Thanks for the advice.

[@neeosstuff7540]

Wow, thanks for the battery help!

[@tinom.2455]

Thanks for this usefull information!

[@actionjksn]

This is good information and I will make sure not to run these things dead. I have a 6Ah and a 9Ah so I will be keeping these things from getting down to 1 bar. Another thing that applies to all of these batteries is to try to keep them in climate control as much as possible. Extreme cold and hot are both bad for these things. I sometimes have no choice but I still try to keep them in a separate bag and bring them in the house instead of leaving them in my truck all the time. FYI the cheapest way to get these batteries is to buy complete kits, instead of bare tools. The kit is usually about $100 more than the bare tool. These batteries cost a lot more than that for these bigger ones. My DCD 999 was $175 for the bare tool and $275 with the 6Ah and a charger. That battery alone is usually about $200 at Home Depot.

[@ShortyzProductionz]

I’ve got a big amount of these batteries and I cycle all them into use rather than use only a couple batteries and I’m glad I do that now after watching this

[@Bob_Adkins]

I think the 20v chargers will balance the cells if left on charge an hour or so after the charger indicates it's fully charged. I wish there were a "balancing" light that would go off when balancing is done.

[@ovalwingnut]

I'm now convinced. Thou shalt not dissemble these dang battery packs. Thank you!

[@briannewhouser154]

Always fascinating.

[@mesmerus]

Matthias, that Torx screw with the dot in the middle is a "Torx Security" bit; they're typically the same sizing, just TT9 instead of T9 in this case.

[@MichaelSchmittMasterMadCraft]

I was going to take my batteries apart soon to try to fix them. I had two dewalt batteries fail on me within a few months of purchase. A 6ah and a 9ah Its a shame but I've lost a lot of faith in the company. I like a lot of their tools but I am about buy off brand batteries to see how they work. What can I loose at this point? Helpful video.

[@patrickmorrissey2271]

Yeah, the security torx bits are very available from the usual sources.... Other than that, great job on this video. That actually makes some sense... A lot more sense than some of the stuff I've heard.... Great job.

[@1pcfred]

Concrete nails are more available.

[@aserta]

It's perfectly ok to replace the 3 broken ones. The only issue is you need to balance them before installation and subsequently test them with a battery tester. I have one of those charging/checking stations and a spot welder, have fixed my batteries plenty of times. Funny thing... whilst one of these packs lasts new for 2~3 years, once they're rebuilt they last much longer. Oldest i've repaired now has 4 years and counting. Obviously, not everyone's cup of tea, but i have the equipment, so i can.

[@jamesmauer7398]

Sounds like a good idea as to what is killing the cells. It would be cool to measure the quiescent current of the circuitry to confirm. With this sort of drain I'd guess dozens of uA.

[@LuisAntolin]

Thanks for the data. Keep it up!

[@fredio54]

Slight correction, the switch has a third position reachable using the shipping cover in which the three banks of cells are isolated for legislative reasons. I wonder if you're right about centre tapping. Usually they chew on the first cell and only chew when active. Hmmmm.

[@Sylvan_dB]

I would have put a single-cell charger on each of the dead cells, current limited to C/100 or possibly C/20 or even C/10 but lower is better. Even from well under 1 volt I've had cells recover and work for years, but usually with some permanent reduction in capacity. I had a 7S20P pack with one of the 20P sets short circuited to 0 volts for an unknown amount of time. Four of the cells had been physically damaged by the short or showed signs of severe overheating. Removing the short and trying to charge the set failed so I separated all the cells. 13 of the 20 are in my scrap pile either because they were internally shorted and would not charge at all or would self-discharge too fast for my taste. 7 of the 20 recovered and have been working well.

[@chris746568462]

I was literally wondering this about these batteries the other day. Like you i thought they were 3 horizontal series strings of 5 cells. I realise they have the BMS on the battery because of the series connection. It's a bit poor if the BMS can actually be the thing that makes an imbalance in the pack. I have alot of these batteries and am going to take the sides off and charge them. My use case is similar where i have them sitting for a period and then need to use them. I rarely ever deplete them fully though.

[@kenibnanak5554]

The important part of the DeWalt battery pack is the end that connects to the charger or device. The magazine holding the batteries isn't crucial and can be replaced by a different one. It should be possible to 3D print a new magazine that will mate with the device connector end while still being user friendly as far as replacing individual cells.