A 5 cell nimh is easy to use, and plenty for a trainer. I would go with this over a 700 mah nicd, as they don't cost tooo much more, and you don't have to worry about voltage after 3 flights. I always check voltage after every flight, since it's easy enough to do.

I switched to life, mainly because you can fast charge them. I often forgot to charge the nimh until it was time to go. I'm pretty sure that a life is safe to charge at 1c, while doing so on a nimh can greatly reduce flight time. Since the battery is always past 50%, at 1c it will charge by the time I'm all set up. Of course I still try to charge a few hours before anyways. The same goes for field charging, you can safely charge in just a few minutes. The balancing is annoying, so I plan to have a extension running just outside of the airplane, and then another from my balance board, which should make it easy enough.

Hubert