Which batteries (mah) for XP2 Transmitter?

[bertberr]

Hi, just bought an RC18T for my son to bash around with, and could do with some advice on the best AA batteries to pop in the TX. I want rechargeable, but not sure if a higher mah rating such as 2100 is necessary, or whether 800 would be OK?

On the AE website it says current draw is 200mah @ 12v??? Not sure how that translates to battery power though??? Advice please!