Power and convenience. The 87151 packs 50% more charging and starting power than most portable chargers, plus features automatic 12-volt settings to shut output OFF at full charge, but turns the unit back on if the battery discharges for any reason. Charges 6 & 12 volt batteries, deep cycle marine batteries and provides reverse connection protection. Great Tools become great sellers because people know they can depend on them to do the job every time. That's why equipment from Century have been top sellers for more than 60 years.