The correct charging voltage for your battery depends on the type of battery you have. Most of today’s automotive and marine batteries are 12 volts, while some motorcycle and lawn tractor batteries are 6 volts. Check the battery or the vehicle owner’s manual to find the correct voltage. The value of the charge rate voltage is determined by the battery manufacturer. Deviating from the recommended values will under or overcharge the battery–both of which will reduce the battery’s life and performance.