Does My Boat Motor Charge My Battery?

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Last Updated on November 17, 2021 by Ellis Gibson (B.Sc. in Mechanical Engineering)

Do you know how to charge your battery? Does your boat motor charge the battery? Do you need a trickle charger or solar panel for a boat? If you enjoy boating and being on the water all day long then it’s important to make sure that your batteries are charged. Read this blog post for tips on charging batteries in boats.

So, does my boat motor charge my battery? Yes. When your outboard engine is running, it produces electricity that will power your boat. This electricity flows into the batteries and makes them rechargeable. The rectifier is a special component that converts the coil output into a regulated DC current suitable for charging the boat battery.

How do outboards charge batteries?

One of the most common questions about outboards is how they charge batteries. The answer to this question has many factors. It can depend on what type of outboard you have. 2-stroke engines use a different charging method than 4-stroke engines do.

Some outboards have a charging circuit, which uses the alternator to charge both the house battery and starting battery. This is an efficient way of powering batteries because it’s possible for one engine to power two batteries at once.

I considered the most popular solution, a solar panel. But after seeing how expensive and difficult it would be to maintain an effective system. In our climate which we sail often, I decided that this wasn’t enough of a fix for our needs.

The winds are usually light at North Idaho lakes during summertime. So when you factor in how much fuel my motor uses while sailing on these days.

Battery Charging Procedure with an Outboard Motor

After going through the cost and complexity of a solar panel system, I considered our outboard motor to charge the battery.

The major components needed for an outboard charge are:

1) An electrical generator has coils that create electricity from a motor’s rotation.

2) A regulator or rectifier converts the pulsating waves of AC current into a constant direct current that is suitable for charging the battery.

I was able to buy a used regulator/rectifier that I mounted in 5 minutes. The last step of the process, connecting it to the battery on board, only took me 3 minutes!

I mounted a heavy-duty waterproof connector in the hull, so that I could disconnect and reconnect my motor easily. It’s as easy as connecting to the gas line which is great because there’s no need for extra drilling. Moreover, I can disconnect the battery in seconds with a couple of quick moves.

I put together a simple 2-wire harness out of 12 AWG cables. One end goes to the rectifier/regulator output, and the other to the ground on the motor; it exits via an accessible grommet at the front before terminating in a male half of a two-pole connector.

I took a 12 gauge duplex cable and ran it the length of my boat from the battery to where I wanted electricity. When I got there, all that was left for me to do was attach one side with an outboard connector so my motor could get power as well!

Once the cables were connected, I used a flame-retardant woven loom to cover all exposed sections of wire. When disconnected from the boat’s battery terminal and gas line, they fold neatly out of sight along with these lines too!

A 10 amp fuse holder was attached to one end of my positive cable where it connects with the battery’s positive terminal while its negative counterpart is connected to a bus bar on which other wires are also connected.

Step By Step Instruction to Charge your Trolling Battery From Your Outboard Engine

Step-01: Mount the battery combiner within two feet of the starting battery. The combiners are waterproof so they don’t need to be undercover and can help improve visibility with LEDs that will not fade when exposed to direct sunlight.

Step-02: Connect one of the red cables to your starting battery’s positive terminal. With a 100 amp connector, both leads can be used interchangeably.

Step-03: Connect the other red lead to one of your trolling battery’s positive terminals. You’ll usually need an extension cable if you want it mounted in the bow, and since all negative terminals have to be connected together with a duplex wire, 12-gauge is recommended for this job. Cut off (or leave) enough length on that terminal so you don’t short anything out!

Step-04: Connect the negative terminals on both batteries to provide a return path for charging currents. This is typically done with black wire in the duplex cable which connects from battery-to-battery, or alternatively by creating an enclosure protecting all connections and wires connecting between them. Be sure not to let any cables get damaged–especially if you have a metal boat!

Step-05: Connect the black terminal lead to your starting battery’s negative terminal. You may want to shorten this one time, but be sure not to cut it too short and prevent a connection!

There’s no need for lengthy leads here, just make sure you have enough slack so that all connections are made correctly.

Step-06: Cut a 2-3 inch length of green wire and secure it with electrical tape to prevent any contact.

You need to make sure you have enough wire in the case that you ever want to connect back up. This is why it’s important not just cut off green wires. But leave some remaining on both ends of your cables so they can be reconnected later if necessary!

Now when the engine is on, a light will let you know that it has connected to your trolling battery. When you turn off the engine, this light goes out and lets you know they are disconnected so your starting battery doesn’t run down while running through waves or currents.

The ability of an alternator in our boat’s motor system (which powers things like electronics) to charge up a trolling battery depends on how much power we’re drawing from other sources. Like using lights for fishing at night–and if too many batteries get drawn upon without any chance for them recharging themselves. Then there won’t be enough charge left over to keep everything going strong once dark falls again.

How do you charge a marine battery with a portable marine battery charger?

Many boats are limited in terms of storage space. So installing a charger is not always possible. For those who have an electric trolling motor-powered kayak or canoe. That doesn’t need to be plugged into shore power for charging purposes.

And don’t want the hassle associated with carrying their boat up onto land every time they would like to charge it then portable battery chargers may make sense as well.

Many people use small boats on lakes without docks – there’s no place near where you can plug your boat in at all times when needed!

You can count on Minn Kota Portable Chargers to keep your battery fully charged and ready for any fishing expedition. Some products in this category provide key features, including digital microprocessor control of the charging process, automatic temperature compensation, and automatic multi-stage charging with LED indicator lights. Both are excellent choices that come at very affordable costs!

How do I know if my outboard motor is charging my battery?

If your engine light is on, you want to make sure the boat battery has a charge. There are two ways of checking:

  1. Without the engines running.
  2. With the engines running.

1) Without the engines running:

To check if your boat is charging the battery, you’ll need to test the volts. Place the multimeter on the Volts scale. Look for a reading of 13.5-14.5v DC when it’s working properly. Anything less than 12.8 volts does not charge the battery. If the boat’s battery voltage is below 12 volts with the engine off, it may take a bit to climb above 12.8. However, if the voltage climbs when operating the engine, then it is charging.

2) With the engines running:

The first step to take in order to charge your depleted boat battery is making sure it’s connected correctly and securely with the power source. Once the engine is switched ON if you notice that your battery has a higher voltage than usual, then congratulations! You’re charging.

If we measure voltage directly at our alternator (not across anything else) with just one wire hooking up right next to terminal G3/G2 we should see that it’s supplying a steady 14 volts with no load (engine running) and then the voltage starts to droop as soon as we turn on any accessories like lights, stereo, etc. This means our alternator is capable of providing enough power for all of these devices and has plenty stored in its internal batteries while driving.

How long does it take for an outboard to charge a battery?

When trolling, a battery will need to be charged by attaching it to a suitable shore charger that can recover the energy for use another day. If I recall correctly, 1 hour of trolling requires 2 hours of charging at say 10 amps, but some people don’t have the time or patience for this!

A float charger can help keep it charged when you’re out on the water and won’t overcharge your battery-the best option is an automatic one that shuts off automatically once the charge level reaches 100%.

However, it only keeps your charged battery up and ready to go so you’re going to need an alternate power source like solar panels if possible in order to keep on top of energy usage.


Although it is possible to charge a battery with your boat motor, this should only be done in an emergency situation. The voltage of the engine will not produce enough power for adequate charging. You may damage your battery if used excessively.

If you are looking to charge a fully drained 12 volt deep cycle battery. Under ideal conditions it would take about 6 hours with a 10 amp charger. It can also take up to 24 hours, depending on how low the level of discharge was before starting the process so patience is key!

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