Battery Size & Charge

[mr.k]

I have the A13-OLinuXino-WIFI, what is the best size battery that the board can use with the LCD touchscreen attached? Would a 6V 2000mAh battery work? How long would it power the device?

Also, I was wondering if connecting the external power while the battery is connected would charge the battery, do nothing, or overpower the board.

[olimex]

the battery should be Li-Po or Li-ion 3.7-4.2V the capacity could be any size