You can charge your batteries then balance them with something like a blinky balancer or use a balancer like this http://www2.towerhobbies.com/cgi-bin...?&I=LXMGS7&P=V
This balancer you put between the charger and the battery and balance as you charge or you can use it by itself and balance afterwards. You just have to make sure the batteries you buy have balance tabs on them (the plug attached to the battery by 4 wires for a 3 cell pack). Different batteries have different style tabs so you have to make sure what you get will work with your batteries. I think Venom, Electrifly (GP), esky and align have the same tabs. I know Thunder power uses a different tab. It is good to always balance your batteries and try not to over discharge to get their full life out of them, but in a hurry I've skipped a balance or 2 and haven't had any problems.