Nintendo switch battery

[DJJK]

Anyone tried to put the battery of a Nintendo switch in a pi project? It’s flat, it’s small, it’s 3,7 V and 4310 mAh. And it’s cheap. But there 5 wires coming out of it. 2 black (-), 2 red (+), and one grey? The + and - wires are probably just doubled for the current handeling but what’s the grey one for?

[Helder]

Possibly for measuring temperature so it can stop charging if it gets too hot.