Not that difficult,the battery Eken come with is loose.Easy to deconnect from motherboard.Cut and strip the leads so you can twist the copper,and then solder.I hope your battery will work,you can give it a try using the Eken charger.
Yes. Mah determines how long your batteries have before recharging. >Mah = more time.Could you mod this with 2 1900ahm batteries that are both 3.7 volts?