Battery balancing

If you search around the site you will find several threads that talk about your question.

 

When it comes to balancing a pack with hobby chargers they will allow you to charge up each module to approximately the same max voltage/charge. But the very best professional battery re-builders will use $15-$30K in equipment to precisely charge each module to the exact same voltage. One of my friends can charge and balance 80 modules at a time with his equipment.

However, between low cost and ultra high cost solutions, is a high voltage trickle charger, often referred to as a grid charger. The cheapest of these provide a high voltage (250V) charge to a prius pack at 1/4 of an amp. The more expensive trickle chargers, like Prolong, which is made by Hybrid Automotive, uses the NiMH charging algorithm to fluctuate the high voltage current in the below 1amp range.

In my experience with working on battery packs, rebuilt packs that get a final charge and balance on the Prolong charger over night tend to be significantly less problematic, than the ones that don't.