How to Charge a Deep Cycle Battery From a Generator

by Paul Richard
dead battery image by Katrina Miller from

Many boats, recreational vehicles and trucks use deep cycle batteries. Deep cycle batteries provide a greater charge capacity than a standard battery, allowing users a longer period of time before re-charging is needed. You can use a generator, either portable or installed in a vehicle, to re-charge a deep cycle battery. Properly charged batteries can have a long, useful life and provide starting or accessory power to vehicles and equipment not connected to another power source.

Step 1

Inspect your deep cycle battery. Fill non-sealed batteries with distilled water to the full mark inside each battery cell. Remove any spilled acid or corrosion from the top of the battery.

Step 2

Fill the generator with gasoline. Check the oil level in the generator according to the manufacturer's instructions. Start the generator and allow it to warm up.

Step 3

Attach the battery charger alligator clips to the battery terminals. Attach the red charger clip to the positive terminal on the battery. Attach the black clip to the negative terminal on the battery. The positive terminal is indicated by a plus sign on the battery next to the terminal, and the negative terminal is indicated by a minus sign. Use a three-stage battery charger to provide a higher charge rate for depleted batteries, a medium-rate charge for slightly discharged batteries, and a float charge to maintain proper voltage for charged batteries.

Step 4

Plug the battery charger into the generator's 120 volt outlet. Confirm that the battery charger is operating by inspecting its charger condition light. Review the battery charger instructions for descriptions of the lights or gauges showing the status of the battery charger.

Inspect the deep cycle battery liquid level periodically, and add distilled water as needed. Do not allow the liquid level to drop below the top of the battery plates, as this will damage the battery and cause overheating.


  • Remove battery corrosion with a paste of baking soda and water. Do not allow baking soda to enter the battery.
  • Charge batteries in a well-ventilated area. Charging produces hydrogen gas.
  • Some generators have 12-volt connections that will permit direct charging of batteries. Use caution when connecting directly to generators, as the charge rate is not controlled and the battery can be overcharged and damaged.


  • Battery acid is corrosive. Wear eye protection and gloves when working with batteries.
  • Always remove the vehicle ground cable from the negative battery terminal first, then remove the positive cable. This will minimize sparks that can cause fires or battery explosions.
  • Never smoke or use open flames around batteries or gasoline-powered generators.
  • Operate generators in well-ventilated areas outdoors. Generators produce carbon monoxide and should never be run indoors.

Items you will need

  • Portable generator
  • Gasoline
  • Three-stage battery charger
  • Distilled water

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