Battery Care

Can I Charge Deep Cycle Batteries with Generator & Is It Safe?

Generators have many benefits, especially when it comes to providing reliable power when the utility power isn’t available. Most generators aren’t sure whether it’s safe to charge deep cycle batteries with a generator.

The short answer is YES. But, it would help if you used a voltage regulating smart charger and an inverter generator. The charger can help provide regulated and monitored voltage as required by the battery. An inverter will provide clean, safe power to the battery charger, making the whole charging process safe for your deep cycle batteries.

Some people do charge the batteries directly using the 12-volt outlet in an inverter generator. But since the voltage isn’t regulated, there is a high risk of damaging the batteries to a critical failure. So, what’s the safest way to charge a battery using a generator between the two? The answer is in the text below – continue reading to understand everything about charging deep cycle batteries with a generator.

What is the Safest Way to Charge Deep Cycle Batteries with a Generator

Many marines, automotive and boats, recreational campers and trucks use deep cycle batteries. They provide reliable, high-capacity power compared to standard batteries. That allows owners to enjoy the charge for a more extended period before the subsequent recharging.

Most people know it’s possible to charge a battery with a generator, but they don’t know how to do it safely. And as you well know, all inverter generators come with a 12-volt DC outlet, sometimes labeled as a ‘battery charger’ outlet.

It’s is mainly intended to provide DC current for running 12-volt devices directly from the generator. It produces unregulated 13.6 volts, which drop when the generator is under load, to around 12.6 volts or even less. The output is, however, enough for running 12-volts lights and equipment to full charge. Why?

  • The DC outlet produces about 8-amps and 13.6 volts of power, too low for full or speedy battery charging. It might take six or more hours to charge a 100-amp-hour deep cycle battery half. And from there, the charging reduces progressively, and it might take over 24 hours to reach 70% and multiple days for a full charge.
  • Another thing, the DC voltage produced in the outlet isn’t regulated. It varies as the generator RPM shifts. The voltage fluctuations are okay when the generator runs a low load but not under a medium or high load.
  • And since you’re charging directly, there is no way to cut down the charging voltage when the battery is nearly complete.

That means hooking your deep cycle batteries to a 12-volt DC outlet isn’t the safest way to do it. The socket might be excellent for running 12-volt devices during an emergency or charging the batteries for a short time to provide a trickle charge. If you demand anything more, you’re potentially risking your deep cycle batteries.

So what’s the Safest Solution for Charging Deep Cycle Batteries with a Generator?

The safest way to charge your deep cycle batteries using a generator is to use a 120-volt or 240-volt battery charger off the respective AC outlets. The method is much faster, safer and accurate.

Another thing, a smart battery charger will regulate itself as the charge build-up in the battery. It has a system that monitors the charging process and prevents the charger from pushing the same amount of amps as the batteries near full.

It’s an excellent plug & play option as you don’t have to worry about checking out the charge to know when the battery nears full. It’s also easy to use. All you need is to get a good quality battery charger, plug it into the compatible AC outlet, and connect 12-volt charging cables with the respective terminals on your deep cycle batteries.

Warning: Remember to check the polarities of the cables and battery terminals to make sure black goes to the negative terminal and red connects to the positive terminal.

Can you use an RV converter to charge deep cycle batteries?

Yes, RV’s converter converts 120-volt to 12-volts, but it’s not designed for charging batteries. It’s mainly used for providing 12-volt power to your RV when the rig is plugged into the AC outlet.

It allows you to run 12-volts appliances and devices in the house and maintain house batteries at a slow rate. However, you must ensure all the appliances are off when charging the generator to charge the batteries.

Note this; if the deep cycle batteries charge is lower than 35%, the generator will take longer to recharge to even 70%. What’s more, plugging the RV to AC power and using the converter to charge the batteries won’t get your battery to full charge. It can only add charge enough to get you by.

Best solution: A fully automatic 3-stage battery charger can charge the batteries faster and improve their performance and lifespan. It’s also available in some modern RVs, and you can also buy an aftermarket model and install it in your RV.

How to Charge a Deep Cycle Battery from a Generator

Recharging your batteries properly improves their performance while extending their lifespan. So, how can you charge your deep cycle batteries with a generator safely?

Step 1: Inspect Your Deep Cycle Batteries

Open the cell caps and make sure the fluid level is at the full mark. If it’s not, get your distilled water and fill them. Don’t forget to wipe off the spilled acid or corrosion from the batteries top.

Step 2: Start Your Generator

Fill your generator with fuel, check the oil level, start the engine and allow it to warm up as you prepare the setup.

Step 3: Connect the Batteries Together

If you’re charging a single deep cycle battery, connect the alligator clips to the battery terminals with the right polarities.


If you have more than one battery, you have three options for connecting them; in parallel, series or both.

Connecting the batteries in parallel:

  • Before connecting the batteries in parallel, you have to make sure they are of the age, charge and voltage. Joining miss-matched batteries in parallel could lead to damages.
  • If you’re sure the batteries have the same features, join all the positives using the red alligator clips and the negatives using the black alligator pins, as shown in the image below.
  • Connect the red cable alligator pin to the first battery positive terminal and connect the other end to the positive of the second battery. Do the same with the next batteries and connect the charger clips to the first battery in the right polarities.
  • The pattern should be: charger + terminal connects to battery + terminal and create a + + + pattern.

Connecting the batteries in series:

• When connecting the batteries in series, you don’t have to worry about age, size and other factors.
• All you have to do is make sure you connect the positive terminal to the negative terminal of the second battery and then to the positive terminal of the third battery.
• The pattern should be: the charger’s negative clip connects to the battery’s + terminal, then the next battery’s – terminal followed by + of the next batter before joining to the positive pin of the battery charge.


Step 4: Plugin the battery charger to the compatible outlet on your generator

With the generator ready and warm, plug in the smart battery charge to either 120-volt or 240-volt outlet depending on its compatibility. Consult the user manual to be sure of the type of outlet to use. Also, review the instructions in the manual for the lights and gauges or settings you might be required to set depending on how many batteries you’re charging.

Step 5: Inspect the Batteries Regularly

Remember to check your deep cycle batteries, especially their fluid levels. Make sure to add distilled water when the liquid level reduces. Never allow it to drop below the battery places, damaging the battery and possibly cause a meltdown from overheating.

Related Questions

How long does it take to charge a deep cycle battery with a generator?

When using a smart charge and 120-volt or 240-volt generator outlet, you can expect the battery to be full in a few hours, depending on the amount of charge it initially had before connecting to the charge. Normally, it will take the longest if the deep cycle battery is below 20%

Why is my generator not charging the battery?

The terminal contacts might be coated with corrosion; the battery might have lost the capability to hold charges, or there could be an issue with the charger or the generator outlets.

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Sharif Gen

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