Hey Terry,
I am running a Hacker competition C50-14XL with the Hacker Opto 99 Speed Control, and I am using a pair of 5S1P Tanic Pack 4350 mah 25C batteries. Tanic Packs made these up special for me with balance connectors for the CellPro 10S charger. I have a pair of CellPro 10S chargers, and I charge the packs at 2C at the field in about 20 to 25 minutes.
You can get more technical information about the Li-po cells in the battery packs at
www.enerland.com.