Battery chargers are used to replenish batteries. They charge batteries in a specific rate based on the type and voltage of the battery. Fast chargers use control circuitry to ensure that the cells do not damage themselves. These circuits can be integrated into the battery cells or separate from the external charging unit. The majority of fast chargers are equipped with a cooling fan to keep the cells at safe operating temperatures. The fast chargers can double as a standard overnight charger as well.
A PNP charger is necessary for a constant current source. Its base will be grounded to measure the charging current. The ISENSE pin monitors the charge current. The BAT pin controls the charging current. Some chargers require an external current sense resistor, but most do not. Most models also require a blocking diode to protect the battery from draining when input impedance becomes low. For best results, select a charger with this feature.
A battery charger that automatically detects its type and charge state can help you save money on batteries. Automatic trickle chargers are ideal for people who do not have time to manually monitor their batteries. These chargers automatically shut off when the battery is full, preventing overcharging. They also come with float battery maintainer modes to compensate for lead-acid battery self-discharge. A battery charger should be able to charge a wide range of batteries.