Self-taught appliance repair ep. 259, replacing a Li-ion battery for a fan, a returning customer whose machine was repaired a few months ago; bought four cells for a few dozen yuan; take it all apart (forgot how, had to look up the old video); the screws are all really loose as if it's been opened, did the customer try a sneaky repair and fail; plug in to charge: shows 0%, how can it be 0%; try an adjustable supply at 5V and it takes charge, 0.4% and charging, so take it apart; easier with last time's experience; photograph the layout and note the polarity (+ − + −...), clean it first then photograph or you can't see and get it wrong. Not sure of the quality of the cells bought, test with the RC3563 tester: about 25–26mΩ, 'paid nearly ten yuan each and the quality's nothing special, paid a fortune'; pull an original cell and it reads 28mΩ, 'his cells are about the same as mine'. Get the AWithZ spot welder out and weld: this side done, now this side, welds beautiful; the nickel strip is a bit too long and can't be cut, add some insulation; trim the next piece, mustn't be too long; the scissors are no good; a few extra welds, tap it down; very beautiful / number one. Test: customer says it runs under a minute after a full charge; put back together and still 0%, could it be reversed?; charge to 60%, unplug and start, seems fine now; time flies, two machines a day, a battery swapped morning and afternoon, when will I ever get ahead. Comments: sort out your polarity first or you'll blow yourself up mate; apprentice; should the four cells be ¥20 each; I laughed when I saw the resistance test; what spot welder is that.