I honestly don't think the capacity was just 400 mAh at 11.1V: that's around the same as a 9V alkaline PP battery. A typo, surely.

Laptop batteries are usually built from 18650 Li-Ion or (more rarely) LiPo of similar capacity. They're usually around 1000-3000 mAh each (@ 3.7V).There are six cells in that Patona one so they're probably wired up 2 parallel/3 serial, which is about 1500 mAh per cell, which sounds reasonable enough.

I think one of the cells had failed and was just being reverse charged by the others as soon as any load was put on the battery, and so immediately crapped out.

[ Edited by KennyR 01.07.2019 - 23:57 ]