DIY 12 Volt Battery Box for Trolling Motors

Building my trolling motor battery box was simple and allowed me to customize it to suit my boat's needs. The quick connect/disconnect posts for the trolling motor leads save me time and get me out on the water much faster. The voltmeter on the box lets me check the status of my battery while also powering devices through the USB and USB-C fast charging ports. When I get on the boat, I simply place my battery box and connect my trolling motor leads in seconds without needing tools—much quicker than wiring up the whole system every time.

When I'm not out on the water, I use this battery box at home as a reliable backup during power outages. It keeps all my devices charged and powers some lights as well. This versatile box is perfect for boats, home backup, RVs, camping, solar setups—you name it!

x1 – Drill

x1 – 1/2” drill bit

x1 – 1-1/4” drill bit (I used a cone bit because it was smoother for drilling plastic)

x1 – 9/16” socket wrench

x1 – Battery Box DIY kit (I am using a Vmaxtanks group 24-31 adjustable box which allows me to use different battery sizes for my other applications. You can use any size or brand for this since this build is customizable).

I used a 12V—100ah battery. For a higher-quality option, I use a Vmaxtanks lithium battery; a budget option would be a LiTime Lithium.

The voltmeter in this kit is compatible with all types of batteries, including AGM, Lithium, gel, etc., in 12V, 24V, and 36V. The battery type and size you choose will depend on the size of the trolling motor (or other application) you use and how much run time you need for each trip.

It is a good idea to measure very carefully where you want your holes to go since this decides where the quick posts and voltmeter get installed.

Beginning with the 1/2" holes for the red and black quick posts, I used a 1/16" drill bit to drill smaller holes first. This made it easier to drill with the 1/2" bit. Proceed to drill the holes with the 1/2" drill bit.

Next, use the 1-1/4" cone drill bit for the voltmeter hole. Notice in the third photo that it is placed higher up on the lid. This is because the voltmeter is about 2" deep and can bump into the battery when trying to close the lid if it is installed too low (not allowing the lid to close properly).

These holes can be placed on other parts of the lid to suit your custom build, as long as they do not bump into the battery when closing the lid.

Grab your red and black quick posts, unscrew the nuts, and remove the washers. Place them in the order as shown in the first photo. This is the order in which they must be installed.

Begin with inserting the red post into the 1/2" hole (from the outside of the lid, going in). While holding it in place, insert the red washer, metal washer, and 4-AWG cable into the red post screw from the inside of the lid. Now screw on the nut and tighten with the 9/16" socket wrench.

The Vmaxtanks posts come with an extra washer and nut for other connections. I do not have any other connections, so I placed the washer and the nut on the same screw and tightened firmly.

Repeat the same steps for the negative post with the black battery cable.

Ensure you firmly tighten the nuts on these posts since these cables will connect to the battery. A loose connection can cause damage to the battery and a major loss of power to your application.

The Voltmeter has an LCD screen that tells you the voltage of your battery, two USB-C ports, one USB port, and an on/off button. If nothing is plugged into the ports, the LCD screen is readable through the rubber cover, which protects the charging ports in case water splashes into the boat (or if it rains).

First, remove the plastic nut from the voltmeter and insert the voltmeter into the 1-1/4" hole. Rotate it so that is aligned straight and in the correct orientation.

Screw on the plastic nut by hand on the back end of the voltmeter. You may have to make one last adjustment to ensure it is aligned straight. Proceed to tighten it by hand until it is tight and does not move around.

Next, attach the voltmeter cables to the metal tabs. Ensure you attach the correct polarity on these metal tabs (red on the + and black on the - ). Right next to these metal tabs, there is a plus sign and a negative sign indicating the polarity.

Now, the wiring in the lid is complete.

We are now ready to wire the lid to the battery.

The battery box I am using is a group 31 size, with the option to use group sizes 24, 27, or 31. A battery's "group size" refers to its physical dimensions. See the battery group size chart attached for groups 24, 27, and 31.

Since I am using a group 27-size battery (smaller than a group 31), there is some room on the left side of the box that can be left empty or used as a small storage space. The Vmaxtanks adjustable box comes with a divider that holds the battery in place, see step-by-step photos for reference.

Before handling the battery, avoid touching the positive and negative terminals simultaneously with any conductive object. Doing so can short-circuit the battery and quickly cause damage. I recommend using a wrench with a rubber handle to avoid a short circuit, unlike the wrench I used.

1. Place the battery in the battery box. If you are using the Vmaxtanks adjustable box with a battery smaller than group 31, place the battery on the right side of the box and insert the divider to lock it in place.
2. Unscrew the positive and negative battery terminal screws.
3. Starting with the positive (red) side, hold the terminal hex screw and place the voltmeter ring cable on. Then place the 4-AWG cable on that same screw.
4. Using a 9/16" socket wrench, tighten this terminal screw into the battery and tighten.
5. Repeat the same steps for the negative (black) side using the black voltmeter lead and the black 4-AWG cable. Make sure these connections are tight and clean.
6. Make sure the voltmeter turns on. Close the lid.

The battery box is now complete and ready to go!

You are now ready to attach the trolling motor cables to the red and black quick posts by hand from the outside of the box; no tools are required to do this.

Charging the battery can also be done by unscrewing the red and black quick posts all the way out by hand and attaching charger alligator clamps (or ring terminal cables) to the exposed screw. This allows you to never have to remove the lid from the box.

This can be recreated using other battery box brands, sizes, and components. I purchased this whole DIY kit from Vmaxtanks for $44.99 and put it all together with tools I have at home.

Please follow my step-by-step photos for further reference. You may also download the A-Z step-by-step photo I created for a quick overview.

Thank you for checking this out. Have fun and be safe!

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