How to Charge a Trolling Motor Battery With Solar

Solar technology has changed the world. Now, with a solar power system, you can get virtually anything that uses batteries or electricity to work. This is why many people don’t mind disconnecting from the electrical grid. Some hook up solar panels to their RVs or move to remote areas. The wonders of renewable energy have now reached vehicles and even trolling motors.

Anyways, don’t get too excited about the prospect yet. Before you set about powering your trolling motor batteries with solar power, you first have to determine the energy requirement of your trolling motor. This will be instrumental in determining how many solar panels you’ll need to charge your trolling batteries. But before that, let’s talk about the factors to consider when charging your trolling motor battery with direct sunlight via solar panels.

Factors to Consider When Charging the Motor Battery With a Solar Panel

Though there are specially designed solar panels for this purpose, a correctly-sized solar panel should do the job, provided you consider the following factors.

Size of the Panel

A trolling boat is typically small, which means it can’t bear the weight of a heavy solar panel. You’ll need to get a small panel for a small boat, but this also means that the battery shouldn’t be severely discharged because this panel will not be enough to charge it.

Charging Duration

The length of time your battery takes to charge matters a lot. That’s why it’s vital to ensure the size or capacity of the solar panel you want to use matches the energy requirements of the battery you want to use. The longer a battery takes to charge, the higher the tendency for battery sulfation to occur. When this happens, the battery will be irreversibly damaged.

Discharge Depth

The depth of discharge means the limit the battery can be discharged to before recharging. Speaking in numbers, let’s say the motor battery has a DOD of 40%, which means the battery will critically need a recharge when it drops to 40%. The trolling motor battery is usually lead acid or AGM, which have similar depths of discharge. The further the depth of discharge, the more power you’ll need to generate from the panels to charge the battery.

How Many Solar Panels To Power the Trolling Motor Batteries

Firstly, you must acknowledge that solar panels for charging trolling motor batteries and other marine batteries come in varieties. To know the right size of solar panels, you have to know your trolling motor battery capacity and ensure the battery has been charged to lighten the energy load on the solar charger.

Secondly, most trolling motors come with powerful batteries, which is why they need to be charged at least partially because it will take a lot of time for a portable solar panel to charge fully. If the battery has already been charged, a 10-watt solar panel can sustain it. The load is lighter on the solar panel because it isn’t actually charging the trolling motor battery. It’s preventing it from depleting its charge.

If the motor battery hasn’t been charged before its connection to solar panels, recharging it will require a more efficient and larger panel.

Let’s say your trolling motor battery capacity is 100ah. You’ll need a 100-watt solar panel (12V) to charge it. This panel has a solar charging output of 30ah. Though the charging duration will vary based on how depleted the battery is, a general estimate will be two days (if the battery is mildly discharged). It may take more than three days (if the battery is severely depleted) with the same panel because it will trickle-charge the battery.

To reduce the charging time, increase the solar panel capacity, especially in cases where the battery’s depth of discharge is more than 50%. Also, the higher the voltage requirements of the trolling motor battery, the higher the solar charging output required, and this will equate to a higher wattage of solar panels.

How to Charge the Battery With Solar Power

  • Get your solar panels and position them in the best spot to absorb enough energy from the sun. Try slanting the panels after picking your spot on the boat.
  • Switch off the motor.
  • Disconnect the battery from the motor.
  • Connect it to the solar battery charger. Ensure the solar panel comes with a connected charger for the battery. The colors of the wire on the battery should match that of the portable charger – black wire on the battery to black wire on the charger and the same for the red wires.
  • To fix the connector, ensure the black wire goes to the negative terminal while the red wire goes to the positive terminal.
  • Switch on the charger to commence the process. This process lasts a long time – several hours at least.
  • At intervals, watch the battery and the charger during the charging duration.

Benefits of Charging Motor Batteries with Solar Power

The Setup is Simpler

When it comes to the use of solar power for this application, you don’t require an inverter, and the charger doesn’t come with moving parts which makes it able to take up less space on the boat.


As you know, solar power is one of the best things to happen to the environment because it gets energy from sunlight for electricity generation, which doesn’t leave any carbon footprint. This is good for environmental sustainability. Damaged solar panels are also easy to dispose of when dropped at regulated recycling locations.

Limitless Source of Energy

The source of solar power is the sun which is an unlimited source of energy for all life on the planet. It’s been sustaining the world for millions of years. With this source, you don’t have to worry about running out of juice like fossil fuels.

Convenient to Use

The solar panel, just like a solar generator, is very convenient for most people to charge their trolling motor batteries because it’s easy to carry around and connect (if you follow the instructions). It’s also ideal for small boats because it doesn’t consume a lot of space.

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