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Resources and info on fixing Milwaukee m18 batteries
#1
Hi Y'all,

I'm looking for some resources on how to replace cells on m18 tool batteries. I haven't been able to find any on this site, or elsewhere. Lots of resources on identifying bad cells, but I'd like to take it a step further.

Thanks!
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#2
It's not clear to me what you are looking for. Generally, if you open one of these you'll find a bunch of cells that have been spot welded to each other, probably with some kind of frame. To fix it, you'd need to break those welds, test cycle each cell and replace those that are bad, or better, replace them all as that will produce a more balanced pack.

You'd need to see what cells they are using and replace with cells that can match the performance (particularly in terms of discharge rate). It's also not particularly easy to solder in replacement cells, and the heat from soldering is going to impact the cell performance (from minor to horrible). It is better to spot-weld again, but that's a price impediment to be sure.

If you have no experience with this, you need to do some learning. Li-Ion cells are quite dangerous when mishandled. A shorted cell or pack can lead to runaway thermal issues that produce a fire that is very, very difficult to stop.
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#3
I’ve found it’s EXTREMELY difficult to repair an m18. They have a spot on the pcb that must remain powered, and if you break that bus to get at the cells it’s a wrap for that bms pcb. So if you do a lil more digging there is a way to keep it powered, but you are a bad man if you can do it. It only cost me one pack, I think I could do it if you wanna donate. This time I’ll solder a lead to the test point after a proper tinning
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#4
(07-13-2020, 03:23 PM)khauser Wrote: [...] It's also not particularly easy to solder in replacement cells, and the heat from soldering is going to impact the cell performance (from minor to horrible).  It is better to spot-weld again, but that's a price impediment to be sure [...]

Worth strong emphasis: not only may soldering to cells degrade their performance, but it may also make them much more dangerous. See the many warnings here to never solder cells (from all the major manufacturers).

(07-13-2020, 04:38 PM)Kcchris816 Wrote: I’ve found it’s EXTREMELY difficult to repair an m18. They have a spot on the pcb that must remain powered, and if you break that bus to get at the cells it’s a wrap for that bms pcb. So if you do a lil more digging there is a way to keep it powered [...]

Laptop packs are the same way: you have to be very careful swapping the cells. If the BMS detects any anomalous events then it may permanently disable the pack (e.g. blow a hard fuse). So it's a bit like open heart surgery: you need to keep the BMS alive during the cell swap and ensure it sees nothing weird (e.g huge voltage imbalances). For laptops it's even worse: once the BMS loses power you cannot reboot it without a proprietary password and software (except for very old BMS boards). But cell swapping can be done successfully as long as you are aware of these matters and are very careful. But you may end up with a very confused fuel gauge if you use different cells.
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#5
(07-13-2020, 04:38 PM)Kcchris816 Wrote: They have a spot on the pcb that must remain powered, and if you break that bus to get at the cells it’s a wrap for that bms pcb.

Thanks! could a dc power source alligator clip onto the bus?
Like the one I've linked to below? Or spot weld a jumper onto the bus to clip onto?

I was hoping I could find a picture or video of exactly where the positive and negative would need to attach to keep the pcn powered.

Thanks everyone!





https://www.amazon.com/Yescom-Precision-...0679&psc=1
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#6
I agree that it is difficult to repair an M18. And it's because the tamper protection they put on.
Basically, if you disconnect the cells and break the circuit, a chip will self-erase and your battery is dead no matter what cells you put in there. You will have proper voltage but it will just not start. So you should keep it powered while you make the replacement and that may be very difficult unless you have a very good adjustable voltage source.

You will have to set the source at the current overall voltage level, increase to the new level and make the replacement, then disconnect the external source.

See this video:
https://www.youtube.com/watch?v=Rp6CUptw5mM

And the 1st comment.
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