The ability to connect two 12-volt batteries to make a 24-volt system is shared among boats and recreational vehicles. This is necessary to power a trolling motor that requires 24 volts.
Since we know we can’t get 12 volts from two 12-volt batteries, we need to convert the batteries to a 24-volt system before the boat’s electrical system can work with the trolling motor.
Dual 12-volt batteries must be wired to provide the correct amount of power in a boat or RV, whether it’s a fully charged 24 volts or a fully charged 12 volts. This post shows how to wire two 12-volt batteries to produce a 24-volt supply.
The basic principle is that when you connect two 12-volt batteries in series, the final voltage equals the sum of the individual battery voltages. If you wire them in parallel, though, you get 24 volts.
In this article, we will discuss in detail and step by step the procedure of connecting two 12 volt batteries to make 24 volts.
How to connect two 12v batteries to make 24v – Step by Step Guide
How to connect two 12v batteries to make 24v
- Step 1
Connect the positive terminal of the first battery to the negative terminal of the second battery with a length of wire, as shown in figure 2 . Wire size should be at least No. 10 AWG (American Wire Gauge).
- Step 2
Connect the negative terminal of the first battery to one end of a switch. If your batteries don’t already have stud posts, you can add them yourself or buy pre-wired connectors that snap into place.
Connect the other end of the switch to one end of another length of wire. This is the positive power connection that will run to your trolling motor.
Make sure you use a switch (which can be purchased at any boating or marine supply store) so that if one battery goes wrong, you can turn off the circuit and still have full power with the working battery.
- Step 3
Connect another length of wire between the other end of the switch and the positive post on your trolling motor. Make sure to use at least No. 6 AWG wire for this connection.
- Step 4
Connect another length of wire between the negative battery post and one side of a second switch. Connect the other side of the second switch to an unpainted metal ground point on your boat or RV. The negative battery post is often made of bare metal and painted over, so you can scrape it with a tool such as a screwdriver to expose the bare metal to make a connection.
- Step 5
Connect another length of wire between the second switch and the negative terminal on your trolling motor. Make sure this connection is made with No. 6 AWG wire.
- Step 6
Go out on the water, turn your switch on and enjoy!
You may also want to connect an ammeter in series with the trolling motor to check how much current is being drawn. If you are drawing too much current, something is wrong, and the batteries are not charging correctly. You should also add a fuse between the battery and the switch to protect your boat’s electrical system if something goes wrong with your wiring.
- Step 7
Put a fuse between the battery and the switch to protect your boat’s electrical system.
How to charge two 12 volt batteries in series
Now that your battery system is wired together, it’s time to charge them up. For this, you will need a 24-volt charger. It is also possible to use two chargers simultaneously but later.
First, remove the clamps from both batteries and plug in the charger. Next, connect the positive wire of the charger to the positive terminal of your first battery, and then connect the negative wire from the charger to the negative terminal of the second battery. If everything is wired correctly, your charger should start charging both batteries.
The charger will keep each battery topped off until one of them reaches full charge. When the charger is plugged in, it splits your batteries into two separate 12-volt systems. You can use either battery or both at once, but you cannot combine them to make 24 volts while charging.
Once they are charged, unplug the charger and replace the clamps on each battery.
How to connect two 12 volt batteries to make 24 volts with a solar charger
Now that you know how to charge your batteries in series, it’s time to find out how to use a solar charger. This is where things can get complicated. Most solar chargers will not handle 24 volts, so you need to connect two 12-volt solar chargers in series.
There are dangers here that can cause your batteries to explode or catch fire if you do not wire the system correctly. If you follow these steps, however, you should be fine.
First, remove all of the clamps on both batteries. Put the positive wire of one solar charger on the positive terminal of your first battery, then attach the negative wire from that same solar charger to the negative terminal of your second battery.
Then take another length of wire and connect it between the positive terminal on your first solar charger to the negative terminal on your second solar charger. Finally, attach a fuse to the wire between your second battery and charger.
Your two solar chargers should be wired in series, which means they will run at a combined voltage of 24 volts. This is high enough voltage to get your batteries charged quickly but low enough not to cause any problems.
Ensure you connect each clamp on each battery securely before charging begins, or you could have sparks or worse.
Charging your batteries correctly is essential to getting the most out of them and prolonging their life. When you know how to connect your trolling motor battery safely, you can enjoy more time on the water without worrying about whether it will start up when you need it most.
Frequently Asked Questions
It depends on whether you are wiring them in parallel or series. Suppose you want to wire them in parallel. In that case, it is as simple as connecting the positive terminal of one battery to the positive terminal on the other and then doing the same for the negative terminals.
However, to wire them in series, things get a bit more complicated. First, you will need to attach the positive wire from one battery to the negative wire of the other. Then you will need to run a wire from the negative terminal on your first battery to the positive terminal on your second. Finally, put a fuse in between this last connection and your trolling motor battery.
It is as simple as connecting the positive terminals of both batteries and then doing the same for their negative terminals.
You will need to connect your two batteries in series first by clicking one positive wire from each battery to one negative wire. Then you will need to attach a wire between the positive terminal of your first battery and the negative terminal of your second, and then another wire from that second battery’s negative terminal to one side of the solar charger.
Finally, connect the other end of that solar charger’s positive side to one of your batteries, with the other end of that same battery attached to the other side of your charger.
Your batteries will charge at the same rate as one bigger battery, but their capacity will be smaller.
It doesn’t matter with most trolling motor batteries but double-checks before connecting your wires. If your box says 24V or 25V, it is likely okay to connect them. However, if your box says 12V or 6V, you will need to make sure they are connected correctly to avoid damaging them.
It takes a bit of work to attach two batteries, but if you can do it correctly, you will be able to enjoy all the benefits that come with having an extra battery. The most important thing is making sure your connections are secure and fuse-protected, so nothing becomes damaged by sparks or too much current.
It might seem complicated at first, but once you know how to wire two 12 volt batteries together and charge them safely, you’ll be ready to make many trips back and forth to the water a little bit easier.
I am Baker Hughes and I live in the USA. I am an electrical engineer and work with 12 Volt products. I want to explore this section more because it is an area of interest for me that has been developed over time. I have 10 Years of experience with 12 Volt products, specifically wiring, installation, guide, reviews, and troubleshooting.