That’s just it, the testing. First, though, you need a reliable supplier of used, surplus, etc. cells. I have that in Battery Hookup. Then you need some tools, I’m a sucker for tools, so I bought some and will build others from cheap Chinese bits. You need a meter to test internal resistance, that’s a critical value to use, over 100-150 megohms and the battery is getting close to being done, then a charger to charge to full 4.2v, then a discharge- capacity measurement with another device. You inspect for obvious physical damage, the temp while charging and discharging, then compare the capacity with the data sheet.
For example I just bought some used powerpacks, 28, 3500ma, Panasonic cells in each for $28.00 each, so a buck a cell. They are rated 3500mah and are testing at 32-400mah so great there, the IR is mostly under 50megohm so great there. These cells sell for about $6-7.00 each! I bought more!!
That’s basically it. I bought modem batteries too. They all had 4 cells in each. 2400mh LG brand cells. Cost $0.30/cell so comparable. More work and just okay cells, I’ll be making UPS batteries from them
Hope that give you an idea.
Oh and it only takes one weak cell to ruin a pack. The amazing amount of energy these things store makes them rather dangerous unless handles properly. If they discharge too far they won’t re-charge, if overcharged they tend to explode. . . So they use some circuitry call a BMS battery management system, to control all that stuff. That’s a very important part of the battery, one of the things it will do is shut down the whole pack if one cell goes bad. This is for safety. It also means you can find packs with one bad and the rest good.
..he died Happy..
