STANLEY BC4009 40 Amp Automatic Battery Charger 40 Amp Automatic Battery Charger/Maintainer Automatically selects charge rate from 0 to 40 AMPS to maximize battery life, charge speed and maintenance 3-Stage high-frequency automatic rapid charge with Float Mode Monitoring 110 amp Patented Engine Start. Helps start most vehicles in one minute. Alternator check provides alternator diagnostics