The Bosch BC3680 36-Volt Fast Charger can charge a spent 36-Volt 4.0 Ah battery in 45 minutes and a 2.0 Ah 36-Volt battery in 35 minutes. This means that users of the most power-hungry of heavy-duty equipment - such as the Bosch 11536 Bulldog Rotary Hammer or 1651 Reciprocating Saw - have power enough to get the job done with little downtime. The smallest and lightest charger in its class powers the cells safely. This unit has battery-protection systems: one is trickle charge - the first 80 percent is very fast, while the remaining 20 percent of the charge is standard speed. Another is a cooling fan to preclude overheating while charging. This charger provides a charging status indicator and it is also compatible with Bosch 18-Volt batteries.