I have a Futaba 7C with R617FS receiver and use from all-battery.com the following two batteries without any problems and without any adapters - they just plug right in!

http://www.all-battery.com/index.asp...ROD&ProdID=166

http://www.all-battery.com/index.asp...ROD&ProdID=886

And they work great! I can easily fly for a couple days with this setup and I have recently flown 36 flights, on a single charge and had over 9.6 and 4.8 volts left in these batteries, albeit some of the flights were short flights.

I always check my voltages between flights though just as a precaution, and I'd recommend you do this as well.