Chargers apply power to the battery where this electrical energy is stored as chemical energy. When the battery pack is fully charged, excess charge is turned into heat inside the battery. Heat is the most damaging force to affect batteries, and the amount of overcharge put on a battery influences how long it will last. They're used in low-priced tools with fixed batteries, which are stored on their chargers. At their low charging rates, excess electricity during overcharge is dissipated as heat at non-damaging levels.
Quick chargers recharge in three to five hours.
These higher-quality battery cells are designed to handle the increased overcharge rate. Again, excess charge is dissipated as heat, but leaving the battery in the charger for a long time after it's full will shorten its life. Fast chargers are the best option for professional-quality power tools. They recharge the battery in one hour or less. At these high charge rates, overcharge would damage or even explode the battery pack.