MEGABOOST Pro Series 4000 Charger/Maintainer Fully Automatic - Detects 6v or 12v battery and switches from "charge mode" to "maintenance mode" when the battery is fully charged Easy to read LED lights indicate power on, 6v or 12v mode, 2 amp or 4 amp charge rate, and battery charge status 2 amp charge rate for 6v battery Select between 2 amp or 4 amp charge rate for 12v battery Overcharge and Short Circuit Protection