Enough with buying battery's from ebay. You do not know what you will get, like said earlier the seller can praise them into heaven about power and safety, but when you run them they suck. Don't risk it and do it right the first time, your spending a huge load of money on the controller and motor anyway, so it
needs good cell's. Not ebay junk IMHO.
Mike has added some lipo batt's I saw.
http://www.rc-monster.com/batteries.php
Apache 5s 18.5v 3700mah LiPo Battery Pack
This will work quite well. 2 of them in serie's for voltage or 2 of them in parralel for double the mah, but at 18,5 volt. Your choice. You do need a good lipo charger for it obviously.
I seriously wouldn't want to waste my money trying to find el cheapo batt's, cause surprise! your truck will not run very good, if at all.