I don't know why you think you will need a larger battery for your A9. I got mine on the 22nd, put on charge with the supplied charger, spent about 2hrs learning the programming and the radio has used less than 40% of the battery. I did not do any transmitting all the while I was setting up some airplanes.

If I decide to use a larger battery, an Eneloop 2000mh will do the trick with no mods to the radio.