Recently, Dave VK2JDS directed me to build a 12v 20/A/hr lithium pack for amateur radio use for portable use when lugging microwave equipment up to a mountain top for DX. We used a discarded Dyson vacuum cleaner 56v lithium pack, because Dyson use high quality 18650 cells, so it is only the BMS boards that fails, therefore you can repurpose and reconfigure the lithium cells as a high current 12v pack with a bit of careful plastic cutting, and a bit of snip and solder of battery tags in the right places, plus adding a new cheap BMS controller board from Ebay, plus remove and discard the temperature sensing boards as shown.
The pics show the original pack, plus the cell pack removed and a chopped up cell pack which can be resoldered in parallel to provide 12v at 20A/hr, once separated you left with four single cells for other projects, and 4 x 12v cell blocks to solder in parallel, keep all ground points soldered, then all 3.7v points soldered in parallel, then all 7v points all soldered together, then all 12v points soldered together, then when ready you solder the 0v, 4v, 7v and 12v points of the new BMS board to the cells, trying to do this earlier in the soldering phase can damage the new BMS board. Check at each step that you still measuring the expected voltage at each parallel point, ie. 3.7v,, 7v and 12v, otherwise you could end up with sparks and smoke.
BECAREFUL not to short out any opposing contacts, as you will get big sparks and smoke. When finished, add a circuit breaker or inline fuse, then tape it up and place in a suitable sized plastic jiffy box as your portable 12v 20V/hr rechargeable battery supply.
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