For those who are still interested.
I just exchanged the battery of my ZEO. Opened it with a kitchen knife, cut the cables of the battery and exchanged it with a 3.7V 100 mAh battery I bought for a few bucks.
Cables were soldered together.
The new battery is a bit bigger then the original one, so I placed it externally on the front of the ZEO and fixed it there with tape. Looks a bit like a bomb now but works likel a charm. It is charging normally on the station. I haven’t tried how long it lasts without recharging since I am a polyphasic sleeper and sleep 3.5 h at max. But my guess would be that it lasts a bit longer since it is bigger then the original one.
bye,
Jonny