I have been using some Duratrax 4800 MAH 7 cell NiMH batteries and those have done very well in my Rustler. Those cost me like 55.oo per battery at a local shop. Granted you also need to make sure your truck can fit those batteries in it or you may have to mod the compartment. The batteries take about one hour to charge if fully discharged but when running and doing a charge on site it only takes about 35 minutes to charge. Run time is pretty good also at about 35 to 40 minutes.

Also as was stated, the Pirannah charger should not be used to charge any battery over 7 cell.