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How to Charge Your Generator Battery in 3 Different Ways?

how to charge a generator battery
Written by Jamie Masterson

A dead generator is a stress-inducing nightmare. You’re already down one power source, now your backup is down. Although a generator creates power, it needs a source to operate.

When the battery is dead, the generator won’t start. The battery gives the motor the spark it needs to start functioning, then the generator keeps the battery charged using residual voltage.

A dead battery doesn’t mean an unusable battery. Most of the time, the battery just needs a jump to get things running again. Here, we’ll be showing why your generator battery is dead and how to jump-start it back to life.

What Causes a Generator Battery to Die

  • Bad charger

Float voltage is the voltage level that the battery needs to be at to maintain the lowest level of power. If the charger has high float voltage, it will overload the battery and shorten the battery’s lifespan. Low float voltage chargers will drain the battery more than they charge it.

  • The fuse has blown

A blown fuse can cause damage to the circuit the battery gets its power from. The battery won’t receive a charge and will drain.

  • The battery is defective

The longer you have a battery, the more likely it is that the battery is defective. Batteries start to degrade and can’t hold a charge is not used for a long time. This also happens with old batteries. If your battery is old or isn’t holding a charge, it’s time to replace it with a new one.

  • Loose terminals or connections

High mineral build-up on the terminals will block the battery from getting charged. Loose connections will drain the battery to nothing if nothing is done. If the terminals are blocked or loose, the battery is prevented from receiving charge from the alternator.

  • High load

If the load exceeds the output capacity, the battery won’t get a charge from the generator because the generator is using all of its voltage providing power. Boat and trailer generators are especially susceptible to this.

  • Defective AVR

The AVR regulates voltage, so if it’s malfunctioning, the battery won’t get the necessary charge.

How to Charge Your Generator Battery?

There are three ways to charge the generator battery. All three methods require a pair of jumper cables, so make sure you have them handy. It’s always a good idea to wear rubber gloves to prevent any loose current from shocking you and protective eyewear.

Most generators protect their batteries against moisture or external damage. They are usually covered and need to be found. Check out the user manual to find out where the battery is located.

Using a portable power source

Portable power sources are essentially batteries that have AC power outlets that you can plug devices into. You can charge the generator battery using the energy from the source. This method requires you have electricity from the grid.

Here’s how to do it.

  • Make sure to top up all the fluids in the generator. This includes things like coolant and oil. It’s important to keep these things filled while charging the battery so everything will work once it’s charged.
  • Remove the battery from the generator.
  • Take the jumper cables and hook them up to the matching color terminals. Red is positive and black is negative. The battery and the power source shouldn’t have any current running through them while you’re doing this. A live current is lethal.
  • Plug the portable power source into an AC outlet and let it charge the battery.

Using a car

This is probably the simplest method and works without help from the grid electricity. You just need to have access to a car to do it. To charge the generator battery, follow these steps.

  • Attach the jumper cables to the car battery and the generator battery. Make sure the cables are on the correct terminal. Both the car and the generator need to be off while doing this to avoid shocks.
  • Start the car. The car battery is now funneling its excess charge to the generator battery. Keep the car running while the battery is charging. As soon as you shut off the car, the battery stops charging.

Using RC batteries

This method is not recommended except for experts or if you are completely stuck without another way to charge the battery. It also requires a little bit of modding to do.

You need to have two 2S or 3S LiPo batteries, a battery connector, and a jumper cable. You can also use a jump box as well.

  • Take the two batteries and connect them to the battery connector.
  • Connect the end of the jumper cables to the battery connector. The current is now live so don’t touch the clamps and don’t let them touch each other.
  • Attach the other end of the jumper cables to the terminals on the generator battery.
  • Turn on the generator. The charge from the batteries should be enough to get the motor running on the generator.


1. How long does a battery take to charge?

Ans. It depends on how much charge your battery is able to hold. A good way to check how long is to look for the CCA number of your battery, then divide it by 20 then add one hour. This is a good estimated charge time.

2. How long does a battery last before it needs to be replaced?

Ans. The average lifespan of a battery is between three to five years. However, a number of factors can shorten the lifespan, so it’s important to take good care of your battery to get the most out it.

About the author

Jamie Masterson

With decade-long experience as a generator technician, Jamie has worked with USA’s top generator manufacturers and suppliers as an independent contractor.

The long years of service to the industry has taught Jamie the ins and outs of troubleshooting, repairing, and maintaining all kinds of generators in home, industrial and outdoor settings.

Jamie thinks this platform is a great opportunity to share his tips and tricks with you so you can make the most of such power equipment for better living.

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