Things You'll Need
Instructions
Locate and open the battery compartment. Set the second battery in the battery compartment beside the first battery. Identify the positive and negative terminals of each battery. There should be a positive and negative wire running from the first battery over to the motor control.
Take the black negative wire and cut in half halfway between the battery and the motor control. Strip a 1/2 inch of insulation off of the ends of both black wire ends that were just cut.
Connect the first black wire end, that runs to the negative terminal of the first battery, to the positive terminal of the second battery. Connect the second black wire, that connects to the motor control, to the negative terminal of the second battery. The connections can be made with alligator clip connectors or wire connectors. This connects the two 6-volt batteries in series to produce a total of 12 volts.