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How do You Charge a Boat Battery With a Car?

How do You Charge a Boat Battery With a Car?

If you’re using any form of the outboard engine on your boat, you’re going to rely on electrical power from your batteries to move in the water. 

There’s nothing worse than trying to start your boat, only to see that your marine battery is dead. 

Whether you’ve left your boat sitting all winter or haven’t touched your boat in a while, forgetting to charge your marine battery can reduce its lifespan. 

Typically, a marine battery needs more charging as the temperature drops, which means it’s vital to keep them charged and maintained during the winter. 

Ideally, you’ll want to charge a lead-acid battery when it gets to 50%. If you use a lithium-ion deep cycle battery, charge it before it reaches below 20%. 

In this article, we discuss whether it’s possible to charge a marine battery with a car and, if so, how you can do it safely. 

Let’s get started! 

Can You Charge/Jump a Marine Battery With a Car?

to jump your marine battery with a car

Yes, it’s possible to charge your marine battery with a car. 

However, if you’re using a deep cycle battery, it must be a 12-volt battery. Using a lower voltage could damage the car and the battery. 

That’s because most car batteries are about 12 volts. Your marine battery voltage should match the volts of the car battery. 

Also, we only recommend jumping your marine battery with a car if you don’t have access to a designated deep cycle marine battery charger. 

Although deep cycle marine batteries and car batteries have the same basic chemistry, the deep cycle battery has high amperage and quick discharge characteristics. It also gives long-term output.

Using a car to charge your marine battery can reduce the lifespan of the battery. The car wasn’t designed to meet the requirements of a deep-cycle marine battery. 

Furthermore, charging with a car means you won’t control the charging current. 

So when is the safest time to charge a marine battery with a car? 

Ideally, the boat battery and car battery should be similar in amperage and size. This reduces the likelihood of damaging either battery. 

Jumping a marine battery car works by connecting the battery terminals together and waiting a few minutes to charge. 

The car alternator is designed to keep the car’s battery charged and power various loads when the engine is on. However, the car alternator can also charge other batteries, like the marine battery. 

When connecting the terminals of the marine battery and the car, always connect the positive to positive and negative to negative. 

Then turn the boat key and check to see if the engine starts. 

How Long Does It Take to Charge a Marine Battery From a Car?

length of time to charge a marine battery from a car

If the marine battery is dead, you’ll need to jump-start the battery. This means disconnecting the leads once the engine starts. 

The boat will begin to charge as normal as you let the engine run. 

The length of time it takes to charge a marine battery from a car depends on the amp rating and amp-hour. 

To calculate the charging time of the marine battery, you’ll need to multiply the battery capacity by the amperage rating of the car charger. 

For instance, let’s say your marine battery has 200 amp hours, and the current charge rate is 50%. This means it’ll need 100 amp hours to charge. So, if the car can produce 10 amps per hour, it’ll take 10 hours to reach 100 amps. 

That’s why many boat owners leave their batteries to charge overnight, ensuring they’re ready to go on their boating trip. 

Although the battery charging times will vary depending on a few factors, you can use a multimeter to check the state of the charge 

Never overcharge the marine battery because it can hurt the battery’s function level.

Since you’re using a car, keeping your engine running all night to charge your marine battery fully is not practical. 

Furthermore, you won’t know if it’ll overcharge. Most portable marine battery chargers have a feature that automatically stops charging when the battery levels are full. 

We advise letting the boat engine run for 20 to 30 minutes to let the marine battery begin recharging. 

That’s because it usually takes twenty minutes for the marine deep cycle battery to be restored back to normal levels. 

How Do You Charge a Boat Battery With a Car?

Optima OPT8016-103 Batteries D34M BlueTop Starting and Deep Cycle Marine Battery

Follow these steps to charge the boat battery with a car: 

  1. Find the marine battery, which should be located near the engine.
  2. Ensure you’re in a well-ventilated area while charging. Never charge your batteries in extreme temperatures.
  3. Inspect the battery for any corrosion on the cables or terminals. If there is, you’ll want to clean them. While cleaning, wear goggles and rubber clubs to protect yourself from potential injuries.
  4. Connect the red clamp of the car alternator to the positive marine battery terminal. It should be labeled with a + symbol.
  5. Connect the black clamp from the car cable to the black negative battery terminal. Essentially, you are connecting the black cable to the black terminal and the red cable to the red terminal.
  6. Start the engine.
  7. If the motor runs normally, you can disconnect the car cables, starting with the black cable and then the red cable.
  8. Let the motor continue running for 20 to 30 minutes, giving it time to recharge.

Marine batteries are best maintained when they’re kept fully charged. You should keep them fully charged after each boating trip to prevent future dead batteries. 


Everyone is prone to running into sticky situations. 

If you’ve already left for your trip and find yourself stuck in nature, the only option you have is to charge your marine battery with your car. Otherwise, you’d have to abandon the trip. 

Luckily, it’s possible to charge a marine battery using a car. We recommend following the steps laid out above to do so safely. 

Now that you know how to jump-start your marine battery, go out there and enjoy your boating trip!