Source
r/18650masterrace•
bathrobehero

Rebuild questions of a dead Stanley Fatmax battery pack

Hey, so one of my packs threw an error on the charger and won't charge but it still works. I took it apart only to see this: https://imgur.com/a/UoArOk4

Not sure what happened there, there's no way it was exposed to water so maybe one of the cell leaked? Either way, one cell in the corner is reading 2.3V while all the rest are reading 3.5.

Under the wrap there's just gibberish (UG8R28 003172). The smaller 5-cell 2 Ah packs have teal Samsung INR18650-20R (M SDIEM 125) so I'm guessing these red ones are similar in specs (edit: I tested one for capacity: 1990mAh). I'm planning on testing them all and use them in other projects if they have low internal resistance and decent capacity. Except for the badly rusted ones.

So I'm planning on replacing all 10 cells but I have a couple of questions. Like should I go with ~3Ah 20A continous discharge cells or with 30A but with around 2Ah cells? I assume I really shouldn't go below 20A cells but I'm not sure 30A cells would give the tool more power. For reference the 2Ah packs are running the tools noticably weaker than the 4Ah packs. I want a compromise of max strength and not so expensive cells, capacity be damned. I've just no idea if the pack/tools would benefit from higher drain cells or it's at its limit with these cells anyway.

Also, what are the chances I can do this and the PCB didn't fry itself when I removed the cells? Guess I could try that easily though.

Thanks!

Edit: ordered a bunch of new Murata VTC5A 2600mAh 25A cells.

Posted Jul 9, 2022, 10:45 AM UTC · edited

182
Ted_Z•

The original red cells are Sanyo's. Take a look at the cell database and you can infer some more details based on the color of the insulating ring on the positive end.

1
grunthos503•

~3Ah 20A continous discharge cells or with 30A but with around 2Ah cells?

capacity be damned

Sounds pretty simple, if your concern is about power and not capacity.

You want cells with the same characteristics as the old cells. But you can't tell from the old cell model number. So go with the detail you do know, right right on the pack case: the old cells are 2ah. Don't put in 3ah cells as replacements.

If perhaps the old cells were 20a, and you replace them with 30a, you aren't wasting money. You're building a pack that will be much less stressed under heavy load, so it will last longer, in years of life.

0