A friend gave me a broken laptop, with no clear problem description. There was no charger, so after rummaging around in my stuff, I found an HP charger that should work. The laptop was fine, but even though it said "charging" and had s an orange LED the battery stayed in 0% ... Reinstalling, BIOS update etc. didn't help, and the only stuff on YouTube was garbage. So it either the battery or the motherboard. Let's disassemble the battery!
So measuring voltage across the cells shows 0V output from the battery, and 1.2V across all cells (they should be around 12V to 16V). So the battery collapsed, it could still be the motherboard though. Anyway, I'm replacing the cells with some others I pulled from some laptops. After removing the old ones, I carefully weld new-old ones back.
This is my very much improvised battery welder. It's the transformer from a microwave, some heavy duty wire and a Sonoff wifi switch which I've programmed to switch on for 200ms and then off when I press the black button. Very ghetto, but it works really great.
Lars Karlslund 
verb (printfJess) 🦄
Kresten Laust