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A trolling motor that slows halfway across the lake is the moment to learn how to charge trolling motor battery while on the water. A solar panel with a controller can put charge back while the boat drifts, and the outboard can do the same while it runs. The steps below show both routes, what to connect, and what to watch.
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How to charge trolling motor battery while on the water: the quick answer
On the water, a 12V solar panel wired through a charge controller to the battery is the simple route: the panel makes power in the sun, the controller keeps the battery from overcharging, and the motor battery gains charge while the boat sits or drifts. The panels in this guide run from 1.8W to 30W, and the larger panels put back more in the same sun. The other route is the outboard: a DC to DC charger takes power from the starting battery while the motor runs and feeds the trolling battery. Either way, the battery type sets the rules: the panels here state compatibility with 12V sealed lead-acid batteries and LiFePO4 batteries, so match the controller to the battery on the boat.
Step 1: Check the battery
Start with the battery on the boat: its voltage and its chemistry. The panels in this guide are built for 12V systems, and the makers state compatibility with flooded, AGM, gel, SLA and LiFePO4 batteries, so a 12V trolling battery of one of those types fits. A controller made for lead-acid chemistry does not always suit lithium, and a lithium setting does not always suit lead-acid, so check the controller stated battery types before connecting. If the battery label is worn or unreadable, the manual for the battery or the motor gives the chemistry and voltage. See what type of battery for trolling motor for the battery types in plain terms.
Step 2: Pick the charging source
Solar is the route that works while the boat sits still. The panels in this guide run from 1.8W to 30W: the Sunway panel is rated at 1.8W and suits keeping a battery topped up, the POWOXI panel is rated at 9W, the ECO-WORTHY panel at 10W, the OYMSAE panel (on Amazon) at 12W, the Callsun pair at 15W, the Voltset panel (on Amazon) at 20W with a smart MPPT controller, and the SOLPERK panel (on Amazon) at 30W with an MPPT controller. A larger panel puts back more charge in the same sun, so pick the largest panel that fits the space on the boat. The Callsun kit is a pair of 7.5W panels, so the pair can sit apart to catch sun from different angles.
| Panel | Watts | Notes |
|---|---|---|
| Sunway trickle charger | 1.8W | Plugs into a cigarette lighter port or clips to the battery |
| POWOXI maintainer kit | 9W | Smart controller; overcharge and reverse polarity protection |
| ECO-WORTHY maintainer | 10W | OBDII plug plus alligator clips |
| OYMSAE portable panel | 12W | Smart controller; suction cup and carabiner in the kit |
| Callsun pair | 15W | Pair of 7.5W panels; IP68; 360 degree adjustable bracket |
| Voltset panel kit | 20W | Smart MPPT controller; IP67; LCD voltage display |
| SOLPERK panel kit | 30W | MPPT controller; 360 degree adjustable bracket |
The outboard is the route that works while the boat moves. A DC to DC charger takes charge from the starting battery while the outboard runs and feeds the trolling motor battery. It needs a run at speed to make power, so it suits a boat that moves between fishing spots rather than one that sits on the spot all day. A portable power station charged at the dock is another option for the ramp: it can top up the trolling battery before launch, but it does not charge while on the water unless it is fed by a panel. For the controller choice, see MPPT vs PWM for boat.
Step 3: Connect the panel through a controller
Never connect a panel straight to the battery: the controller sits between them and stops the battery from overcharging. The POWOXI, SOLPERK, Callsun, OYMSAE and Voltset kits include a controller in the kit, so the panel, controller and battery connect in that order. Alligator clips go to the battery terminals, or the panel plugs into the cigarette lighter port where the maker states that connection. Keep the connections dry and out of bilge water, and keep the panel where sun lands on it rather than in shade under a seat.
Check the controller lights to confirm the charge: red for charging and green for a full battery on the SOLPERK and OYMSAE controllers, with blue for a connected panel on the SOLPERK controller. The POWOXI controller (on Amazon) uses red for light detection and green for active charging. The Voltset kit adds an LCD voltage display that reads from 4.5V to 60V, so the state of charge can be checked without guessing. If no light shows, check the clips and the panel angle before assuming the battery is at fault. See the best MPPT charge controller for boat picks for controllers with this wiring.
Step 4: Watch the charge and mind the sun
A panel only makes power in the sun, so angle matters more than anything else on the water. The SOLPERK, Callsun and Voltset kits include a 360 degree adjustable bracket, so the panel can be tilted toward the sun as the boat moves. Shade from a seat, a canopy or a rod holder cuts the output, so keep the panel clear while it charges. Check the controller lights through the day: a green light for a full battery on the SOLPERK and OYMSAE controllers means the battery is topped up, and a red light means it is still charging.
On a cloudy day the panel still makes some power, and the Sunway and OYMSAE makers state their panels work well even on cloudy days. Expect less charge than in full sun, and leave the panel connected longer. A panel left connected overnight can drain a battery if the controller lacks reverse-current protection, so check that the controller cuts off reverse current at night: the SOLPERK maker states its controller does.
Ways to make the battery last longer
- Run the motor slower. A trolling motor draws less at low speed, so the battery lasts longer across the day.
- Keep the panel in the sun. Tilt it with the adjustable bracket as the sun moves, and keep it clear of shade.
- Charge at the dock too. Top the battery up with a charger at the dock before launch, so the on-water charging only has to keep up.
- Keep connections clean and dry. Wipe the clips and terminals, and keep them out of bilge water, so the charge is not lost to corrosion.
FAQ: power away from the grid
Can a solar panel charge a trolling motor battery while on the water?
Yes. A 12V solar panel wired through a charge controller feeds the battery while the boat sits or drifts in the sun. The panels in this guide run from 1.8W to 30W, and the 30W SOLPERK panel with an MPPT controller is the largest panel in this guide.
What size solar panel do I need for a trolling motor battery?
It depends on the battery and the sun. The panels in this guide run from 1.8W to 30W: a small panel suits keeping a charged battery topped up, while a larger panel puts back more charge in the same sun. Pick the largest panel that fits the space on the boat, and check that its controller matches the battery type.
Can I charge a trolling motor battery from the outboard while running?
Yes, with a DC to DC charger that takes power from the starting battery while the outboard runs and feeds the trolling battery. It only charges while the boat is moving at speed, so it suits a boat that moves between spots rather than one that sits still all day.
Does a solar charger work on a cloudy day?
Yes, with less output. The Sunway and OYMSAE makers state their panels work well even on cloudy days, so the battery still gains charge, just more slowly. Leave the panel connected and in the clearest light available.
Do I need a charge controller between the panel and the battery?
Yes. The controller stops the battery from overcharging and, on the SOLPERK kit, cuts off reverse current at night so the panel does not drain the battery. The POWOXI, SOLPERK, Callsun, OYMSAE and Voltset kits include a controller, so the panel connects through it rather than straight to the battery.
Related solar guides
See the what size battery for trolling motor, the best marine solar panel kit for lead acid battery and the marine battery maintenance guide.
