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I have been given an old car jump starter pack with an inverter and tyre pump, the gel cell 17Ah battery is defunct.

I also have an 80V 4Ah battery from a mower that is beyond repair as the control board is defunct.

Assuming the battery consists of standard Lion cells I should be able to construct a battery with 5 cells in series adding cells in parallel to add capacity.

Where can I find a BMS that can prevent over discharge, keep cells balanced and prevent overcharging?

“12V” li-ion batteries tend to be 4s. Loads of these on the usual places to get Chinese stuff. Just make sure the BMS is rated for the current or use a small one with a relay.

Thanks.

If I use a 40A 4S one for things other than jump starting would it be possible to bypass it for jump starting or should I just use it as a power pack?

openspaceman wrote: ↑Thu Apr 20, 2023 8:26 pm Thanks.

If I use a 40A 4S one for things other than jump starting would it be possible to bypass it for jump starting or should I just use it as a power pack?

You can do whatever you like! You can have the electric going through the BMS for normal power pack operation or access the terminals directly for use as a jump starter.