Power and Price. The 87121 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, provides reverse connection protection and charges deep cycle batteries. 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.