Got a couple of battery packs in the garage that have failed - one while I was hammering down a descent and one while charging. Each contains 4* 18650 cells. It's occurred to me that I could possibly consider taking apart the existing packs, find and remove the duff cells, then use the remaining cells to make up a new battery. If only one cell has failed in each it might even be possible to make up a 6 cell battery giving me a longer life battery.
However, it's far more than 20 years since I did GCSE science and while I'm ok with the basics of soldering I can't quire recall the specific of series vs parallel when connecting the cells, and am a little wary of shorting anything out and killing more cells while disconnecting /connecting cells. Can anyone offer any useful, practical advice? Failing that, relevant gifs or amusing videos will also be appreciated