I have had some very good results with the [link=http://www.eneloop.info/]Sanyo Eneloop[/link] NimH-batteries for use as Tx and Rx batteries. They are AA sized with a capacity of 2000 mAh and differs from ordinary NimH batteries in that their self discharge is very low.
This is a real advantage for me during winter time when the time between flying sessions can be anything from a couple of days up to more than a month.
With the Eneloop batteries I charge the batteries after each flying session and then just leave them until next time. There is no need for trickle charging or topping up the batteries before use as is the case with ordinary NimH or NiCd batteries.

The only problem is that it is dificult to locate assembled Tx- and Rx-packs. I have bought loose cells and asked the shop to assemble them into packs for me.