Build some high capacity LiPo packs yourself. May not be the prettiest looking ones around, but will be good backup. I've gots lots of site info on packs and smart chargers if interested.

Check out the one in the top left. That oughta run it for a bit.
This and other ones have built in cell balancers, overcharge protection etc.

http://www.all-battery.com/index.asp...S&Category=262

Here are some chargers etc.

http://www.hobby-lobby.com/chargers_lipoly.htm