Peak chargers are used to charge a battery pack at higher rates than the overnight charger. They detect when the battery pack has reached the point where it won't accept more charge and then shut down. If they did not sense the shutdown point, your battery packs would be damaged.

If you're charging at higher rates, you will usually get LESS charge in the pack than a slow, overnight charge will. That's not a problem if you use high-rate peak chargers at the field to keep the packs topped off.