How to Use 12V Battery Charger to Charge a 6V Battery

Updated February 20, 2018

Battery chargers are used to maintain the electrical charge on a secondary cell battery. As a battery discharges, the electrolyte in the battery combines with the electrode material, causing crystal formations. Battery chargers reverse the chemical reaction which creates the crystals, thus rejuvenating the battery. For a battery charger to work properly, the charger voltage must be the same as the battery voltage. Applying too much voltage to a battery will cause the electrolyte to overheat, and will damage the battery. With a few modifications, a lower voltage (such as a 6V) battery can be charged with a larger (such as 12V) power source.

Snip the battery clamps off the charger, leaving approximately four inches of wire on the battery clamp. Mark the wire that formerly went to the positive battery clamp by placing a piece of electrical tape on it. Strip the snipped ends of the battery clamp wire and the battery charger wires of about a half inch of insulation.

Solder the positive battery charger wire to one of the leads on the first resistor. Cover the soldered joint with electrical tape when the joint cools. Solder the free lead of the first resistor to jointly to one of the leads on the unconnected resistor and to the positive battery terminal wire. Cover the joint with electrical tape when the joint cools.

Solder the free lead on the second resistor jointly to the negative battery terminal and the negative battery charger wire. Cover the soldered joint with electrical tape when the joint cools.


Some regulated battery chargers require the battery to possess a certain voltage (typically 9V or more) before the charger turns on. Read the charger instruction manual before modifying the battery charger.


This modification is intended for trickle chargers only. Damage to the battery, the charger or the electrical resistors may occur if this modification is performed on a quick-charger. Battery chargers produce 1 Ampere or more of electrical current, which causes electrical components to heat up. Use caution when removing the charger from the battery.

Things You'll Need

  • One 12V DC battery charger with battery clamps
  • Two 100Ω (ohm), 5W resistors
  • Electrical pliers
  • Vinyl electrical tape
  • Soldering iron and solder
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About the Author

David Sandoval has served as a trainer and technical writer since 2000. He has written several articles online in the fields of home improvement, finance, electronics and science. Sandoval has an Associate of Applied Science in microelectronics from Northern New Mexico College.