Can You Charge a Home Battery With a Generator?

Many homeowners buy home batteries and connect them to their solar panels for recharging. However, what happens if you want to charge a home battery with a gas or propane generator? Find out below if this is possible.

Can a Generator Be Used To Charge a Home Battery?

Yes. A 240-volt battery charger connected to the generator’s AC output is the most efficient method to recharge your home battery. This will allow the battery to be recharged more quickly and precisely. The charger will not be pushing the same number of amps as the battery charges since most chargers regulate themselves down.

Generators can also charge solar batteries using the same approach. Connect the generator AC output to your battery charger, and connect the charger to your solar battery.

How To Charge a Battery With a Generator

  1. To begin, place your generator near your home battery. A few feet from your battery unit, on a flat area, is the ideal location for your generator.
  2. Turn on the generator.
  3. Attach the battery charger to your battery.
  4. Connect the generator to the battery charger.
  5. Charge your home battery to the recommended level.
  6. Turn off the charger when your battery is topped up.
  7. Turn off the generator.

How Long Does It Take a Generator To Charge a Home Battery?

You can use this fairly simple formula to figure out how long it will take to charge your home battery:

Battery Capacity in Amp Hours (Ah) / Charge Current (Amps) = Hours to Charge Battery

Let’s assume for example that you have a 12 kWh, 12 volt, 1000 Ah lithium iron phosphate (LiFePO) home battery bank.

Let’s also assume you’re planning to install a Generac 14kW generator with rated capacity of 58.3 Amps. How long will that generator take to charge your home battery?

Plugging your numbers into the formula above gets you this result:

Battery Capacity of 1000 Ah / 58.3 Amps charge current = 17.15 hours charge time

It’s important to note that this is just a rough number. The transfer switch and inverter / charger powering your home battery can lose a significant amount of amperes on the way from the generator to the battery cells. Heat losses can be significant when charging a large battery bank. The generator itself can vary in output, as well, depending on the load.

Home batteries can also be limited by their ability to receive high amps and turn that into electrical charge, rather than heat losses. Overpowering a small battery with low charge rate capacity using a generator with high amp output will not result in faster charging — instead it will result in heat losses and lower battery life (or worse – a melted battery). It’s always important to match the rate of generator output to the capacity of your home battery to receive it.

Here are some highly rated generators suitable to charge a home battery system:

Generac Guardian 24kW Home Standby Generator with Transfer Switch (Wi-Fi Enabled)

DuroMax XP12000EH Backup Generator 12kW for Home or RV – Gas or Propane Dual Fuel

Westinghouse 12.5kW Dual Fuel Home Backup Portable Generator

As an Amazon Associate, SelectSafety earns commissions from qualifying purchases made through links in this post.

How Long Does It Take To Charge a 12v Battery With a Generator?

A flat 100 Ah lead-acid or AGM battery may be charged to half its capacity in about six hours. It may take up to twenty-four hours to charge it to over 70%.

What Size Generator Do I Need To Charge My Battery Bank?

Generally speaking, the generator should be double the continuous output of the inverter that charges your battery bank. An inverter that produces 4,000 watts should be used with a generator that produces 8,000 watts. In order to power all the loads and charge the battery bank, an 8kW generator would be a good starting point for powering the generator.

What Size Generator Do I Need To Charge a 12 Volt Battery?

To charge a 12-volt RV or automotive battery, you should use a generator with at least 3500 watts and 8 amps of output. Getting a more powerful generator may speed the charging time, but 3500 watts should be enough.

Charging a Tesla Powerwall

Can I Charge My Powerwall With a Generator?

Yes. Installing a Powerwall next to an automated or manual transfer switch coming from a generator is common practice. Tesla may discuss possibilities with you as part of your system design. If you have a backup generator, you may still use it to power your Powerwalls in the event of a blackout.

Can You Charge a Tesla Powerwall 2 With a Generator?

Yes, it is possible to charge a Tesla Powerwall 2 with a generator. A Powerwall should not be directly connected to a generator — the power from the generator must run through a transfer switch which is sized appropriately for the expected load. This may be from your home’s appliances, or from charging the battery bank, or both.

Using solar power to charge a Powerwall situated between the utility meter and a transfer switch is more common than using a generator.

Charging Batteries With Different Types of Generators

Can You Charge a Battery With an Inverter Generator?

Yes. For example, if you are using an inverter generator (for example with your RV), it can charge your battery bank, and it can power any 120-volt appliance.

Can You Charge a Battery With a Gas Generator?

Yes. To charge the batteries, all you have to do is start the generator and turn on the electricity. The transfer switch is already incorporated into the inverter.

Can You Charge a Battery With a Portable Generator?

Yes. A portable generator is the same or similar in function to a fixed primary / standby / backup generator. However, many portable generators are small and meant to only power a few tools or small batteries. If the amps required to charge your home battery bank are significant, then you would want to have a large portable or fixed generator to match the load.

Charging the Generator’s Internal Battery

Most generators have their own internal batteries. These are usually lead acid batteries. The purpose is to start up the generator and deliver sparks to the cylinders to ignite the gas, diesel, propane or LNG fuel.

Does a Portable Generator Charge Its Own Battery?

Yes. While the generator is operating, the battery in the generator is being recharged. Starting the engine drains the battery, thus a portion of the generator’s power is used to recharge the internal battery. The generator must operate for a while to resupply the battery’s power.

What Kind of Battery Does a Generator Use?

Most generators use lead-acid batteries.

How Often Should You Charge a Generator Battery?

At least once a month, the battery should be charged for 24 to 48 hours in preparation for use.

Before putting your portable generator away, make sure the battery is completely charged. Keep the generator running for at least a few minutes at least once a month. It will keep the generator running smoothly and oiled.

Here are some excellent lead-acid batteries for your generator if you need a replacement:

Weize 12V 12Ah Sealed Lead Acid AGM Deep Cycle Battery

Interstate Batteries 12V 35Ah Sealed Lead Acid AGM Battery (SLA1155) with Flag Terminals

Mighty Max 12V 9AH Sealed Lead Acid AGM Battery (ML9-12) with F2 Terminals

Other Related Questions

What Charger Is Best for a 12v Battery?

Use a generator-powered smart charger (230V–12V). Depending on the status of the battery bank, a smart charger employs three or more steps to precisely charge it.

Does My RV Generator Charge My Coach Batteries?

Yes. Your RV’s generator and shore power are the primary sources of electricity for your batteries. You may utilize the electricity from your generator to recharge your RV’s house batteries while it is operating via a converter or inverter.

Can You Jump a Car Battery With a Generator?

If you have the right kind of generator, you may use it to jump-start your automobile. To get the best results, you’ll need a generator with an electric start.

How Do You Charge a Deep Cycle Battery With a Generator?

Generators may be used to charge deep cycle batteries. Your deep cycle battery should be inspected. It’s time to fill up the generator. To charge the batteries, use alligator clips to connect the charger to the terminals of each battery. Connect the battery charger to the generator’s 120-volt outlet for power.

This video should help you understand further how a generator can be used to charge a home, RV or automotive battery:


While it is possible in many cases to charge a home battery with a generator, there are a few things to consider before doing so. First, check with the manufacturer of your home battery to see if they recommend or approve connecting a generator for charging. Second, be aware that some generators produce “dirty power” that can damage sensitive electronics like home batteries. If your generator produces dirty power, this could end up damaging the battery.

Related Tags

  • home battery backup power supply
  • charging powerwall from generator
  • off-grid battery bank with generator

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Nick Klamecki, Author
About Nick Klamecki, Author

Nick Klamecki is a certified Fire and Workplace Safety expert with 15 years experience in product research and testing. He has a degree from U.C. Davis, is an active outdoorsman and spent years ensuring the safety of special needs children. Nick researches and tests workplace, industrial and safety products and provides advice on their safe use. Learn more about Nick here or connect with him on LinkedIn | Medium