It all depends on how the single 12v 3A packs were used before you made them into larger packs.

Basically the cells need to be matched with each other so that they will all be at the same point of charge/discharge at any one point in time. When you first attached the packs in parrallel, were they matched in charge?

If want the packs to last a reasonable life you should seek having them professionally matched/zapped (whatever they call it...) before coupling them in parrallel for charging/discharging.