Gameboy Color and GB Pocket Lightsaver (Light) No Batteries Required Great For Playing In The Dark Or Low Light Areas. Made By InterAct.
For Lithium battery expansion board:
Battery capacity: 3800mAh
Maximum output current: 1.8A
Output voltage: 5.1V ± 0.1V
Standard charging current / voltage: 1.2A/5.0V
It's convenient to power on / off raspberry pi via battery swith;
It can last about 9 hours if only pi 3.
The Lithium battery expansion board can be also used on cellphone.
Note: You can still charge this battery even if the switch is turn off;