Depending on the charger, it will usually charge the batteries to full capacity, then fully discharge them and, finally, fully recharge them to capacity. I don't know the exact physics behind it but I believe that will refresh and get rid of any residual charge "memory" that the battery may have. I've had a set of rechargeable AA's for years that I cycled like that when I got a good charger and the batteries' capacity went from around 1500-1600 mAh per charge to over 2000 mAh. The process definitely put some new life in them.