More Upcycled Power Banks
Here's a quick way to test 18650 lithium-ion cells recovered from laptop battery packs using the simplest power bank enclosure. Put them on charge to 100% then leave for 24 hours and test with the voltmeter to see which ones are holding 3.7 volts or close to it. I have a bunch of old laptop batteries, all with 6 cells each and hoping to recover 16 usable ones for a monster power bank which can be charged at night on cheap electricity (as a wack experiment really, not going to run the tumble dryer obviously!). So far, so good, pack charged to 100% from zero in about 7 hours. Another batch of cells being charged. Cells resting waiting to be voltage tested after about 14 days. Any cells holding a charge of 3.7 volts or more are usable and will go into a power bank casing.