The Bosch BC3680 36V Fast Charger can charge a spent 36V 4.0 Ah battery in 45 minutes and a 2.0 Ah 36V battery in only 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 compatible with 18V Bosch batteries as well.