How To Charge A Boat Battery [Dual & Single]

One of the most important aspects of owning a boat is learning how to charge its one or ma many batteries.

Charging a boat battery ensures that your boat has sufficient starting power and keeps electronics running smoothly.

There are several ways to charge a boat battery and things to keep in mind that we’ll cover in this post.

How To Charge A Boat Battery

The best way to charge a boat battery is with a smart battery charger (Amazon Link Ad). You want to use a smart battery charger, as it will turn on and off as the battery needs it and does all the thinking.

Here are the steps you should take when charging a boat battery.

  1. Disconnect the battery or turn off the battery switch.
  2. Connect the positive of the battery charger to the battery.
  3. Connect the negative of the battery charger to the battery.
  4. Plug in battery charger into the correct wall outlet.
  5. Wait for the battery charger to power up and let you know it’s charging the battery. Follow directions on the battery charger, as extra steps may be needed, especially if the battery is really flat.

Things to Keep in Mind When Charging a Boat Battery:

  • Make sure you use the correct voltage for your boat’s battery.
  • If using an onboard charger, make sure that power supply meets requirements of your specific boat battery.
  • A good practice is to periodically check the water levels in your boat’s battery and fill up when needed. Only do this for batteries that need it, sealed batteries don’t need water added.
  • Make sure you don’t overcharge your battery, as this can cook the battery which is bad.
  • When storing a boat during winter, it’s important to keep the batteries charged, so they last longer.

Battery Hookup Order Matters!

When connecting the battery charger, you must connect the positive first, then negative.

When disconnecting the battery charger, you must remove the negative first, then the positive.

It’s easy to remember, when adding the battery you do positive first, and removing a battery you do negative first.

How Often To Charge A Boat Battery?

Boat batteries, and most lead-acid batteries, go bad due to not being used.

If you’re driving your boat at least once a month, then there is no need to charge it.

If you’re letting your boat sit for more than a month, then it’s best to keep it on charge with the proper battery charger or charge it the night before you want to ride.

With the large size of most boat batteries they can go even longer without being used, but generally one month is a safe standard to go off.

Solar Battery Chargers

Another option to consider is using a solar battery charger that you keep on your boat all the time.

A 5-watt or less 12-volt solar charger (Amazon Link Ad) is just enough power to maintain your battery and keeping it from going flat.

The biggest reason why boat batteries die is due to inactivity, and a solar charger will supply just enough power to keep it active. But you must not go above 5-watts unless you have a charge controller, as you run the risk of over charging your boat battery.

Why Do Boat Batteries Die So Quickly?

Boat batteries die quickly because they are not used often, jet skis are even worse because of their smaller batteries.

If you’re using your boat a few times a month, then you’ll be fine. If you do this and still experience problems, it’s best to check the water levels in the battery or test it with a multi-meter. I’ve even seen loose battery cables cause all kind of problems, especially when starting.

Switching the battery switch to off is not good enough. It’s a common misunderstanding that there is a slight draw from the engine that kills the battery. While there is some current draw, the bigger problem is the battery sulfates due to inactivity, and that is why boat batteries die so quickly.

Can You Jump Start A Boat Battery?

You should never jump a boat battery from a car or another boat, as the charging systems from each could either hurt the boat or the car.

You can jump from another battery or jump pack.

Battery jump packs are great, but the biggest problem is that they need to be charged themselves. So unless you keep one on charge all the time in your truck, it’s kind of pointless as it too will be dead when you need it.

There are super capacitor jump packs (Amazon Link Ad) that I only use as they can sit empty for years and will charge themselves off your dead battery. It takes a few minutes to charge, but it’s charging from the dead battery, or your truck’s 12-volt plug, and will supply enough power to jump start the boat. I know it sounds crazy, but it’s a real thing, and it’s saved me a few times as it’s the only thing I carry now in my truck.

How Long To Charge A Boat Battery?

Most chargers will show when the battery is fully charged, but generally, it takes about 8 to 12 hours for your battery to be fully charged.

It’s also important to use a charger with an automatic shut off feature, like a smart battery charger, so it can turn off and on as the battery needs it.

The best thing to do is use a smart battery charger and leave it overnight. Low and slow is the best way to charge a boat battery, especially if it’s new or drained way down.

What Amps To Charge A Boat Battery

For best results, you should use a 2-amp battery charger rated for your batteries. Most boats use a 12-volt system, so 12-volts at 2-amps make for the best battery charger.

The amps of the charger decide how quick the battery chargers, so a 10-amp charger will charge faster than 2-amp. When it comes to lead-acid batteries, it’s best to charge slow, especially if it’s a new battery. Pushing a lot of amps out will charge it quicker, but could damage the batter and more likely to give you less capacity.

If you use a smart battery charger then going with the higher amp 5 or 10 amp is fine as they do all the thinking and maintaining that is needed. If you’re ever in doubt, go with 2-amps if you’re uncertain if it’s a smart battery charger.

What Type Of Battery Do Boats Use?

Boats will use many types of batteries, some with multiple batteries.

The most common is a size 24 battery rated at 12-volts. This size battery comes in two configurations, starting and deep cycle.

If your boat has two batteries, then one will be for the starting battery and the other for the deep cycle battery. The starting battery is used to start your engine, as it needs a lot of power quickly. The deep cycle is for running things like your radio or anything low power but over a long time.

When sitting with the engine off, you switch to the deep cycle battery to save on your starting battery. When the deep cycle battery dies, or it’s time to go, you switch to the starting battery and run the engine. Once running, you can turn it to both batteries to charge the deep cycle, but it’s not a fast charging system.

Charging Dual Boat Batteries

If your boat has two batteries, you have a different situation when it comes to charging your batteries.

You can set the battery switch to “both” or “all” and connect the charger to one of the batteries and both will charge, but I suggest you don’t.

You need an actual 2-bank charger (Amazon Link Ad). You can buy battery chargers that will charge both batteries separately, and that is what they need. Set the boat battery switch to off for both batteries and connect the dual battery charger up and charge your batteries that way.

While both batteries maybe 12-volts they often have one starting battery and one deep cycle and both will work together when they need to, but they really don’t like each other and take charging differently. For best results, you turn the battery switch off and charge each battery separately using a multi-bank charger.