A 24V trolling motor uses two 12V batteries in series: join one positive to the other negative, then connect the motor to the free terminals.
For the full breakdown, see our best Batteries For 24V Trolling Motor guide.
What Does Wiring in Series Mean?
Wiring batteries in series stacks their voltage while keeping the amp-hour (Ah) rating of a single battery. Connect the positive terminal of Battery 1 to the negative terminal of Battery 2 using a short jumper cable. The remaining two terminals—Battery 1’s negative and Battery 2’s positive—become the output posts for your motor. Two 100Ah batteries in series give you 100Ah at 24V, not 200Ah. Parallel wiring doubles capacity but keeps 12V, a common mistake that leaves you with a motor that won’t run.
Use batteries with matching voltage, capacity, and chemistry throughout. Mismatched pairs charge at different rates and shorten the life of both.
Step-by-Step Wiring Guide
Position and Prepare the Batteries
Place both batteries as close together as the compartment allows, facing the same direction so the terminals are easy to reach. Confirm each is fully charged and the terminals are clean—use a wire brush if you see any crust or dullness. A clean connection means less voltage drop under load.
Run the Jumper Cable
Use a short jumper made from the same gauge wire as the motor’s main power leads. Connect Battery 1’s positive terminal to Battery 2’s negative terminal and tighten the nuts firmly. A loose jumper causes heat and intermittent power loss.
Connect the Motor Leads
Run the motor’s positive lead to the open positive terminal on Battery 2 (the bank’s outer positive post). Connect the negative lead to the open negative terminal on Battery 1 (the bank’s outer negative post). The motor now sees 24V between its two power wires. Double-check polarity before powering up—reversing it can damage the controller.
Install a Circuit Breaker
Place a breaker or fuse on the positive lead as close to the battery terminal as possible.
Test Before You Go
Use a multimeter across the bank’s outer terminals—you should see 24V or very close to it. Run the motor at each speed and feel the connections for heat. Tighten any warm terminal and recheck the breaker mounting before heading out.
Common Mistakes and Safety Tips
The biggest error is wiring the batteries in parallel instead of series—you get 12V and the motor won’t run. Reversing polarity is the second most common and can damage the motor controller. Always confirm bank voltage with a multimeter before connecting the motor leads.
Undersized cable is another frequent problem. Secure all cables with clamps or zip ties and avoid sharp bends where chafing could short the system.
Mount the breaker within reach and label the bank clearly so anyone working on the boat knows the terminals are live at 24V.
FAQs
Can I use two different brands of 12V batteries in series?
Yes, as long as both match in voltage, capacity, and chemistry. Dissimilar batteries charge and discharge at different rates, which reduces overall performance and shortens the lifespan of both packs.
What gauge wire should the jumper be?
Match the jumper gauge to the motor’s main power lead gauge and size for the actual routed distance.
Do I need a fuse between the two series-connected batteries?
The critical protection is a single breaker on the positive output lead near the battery terminal. Some setups add a fuse on each positive post, but the main breaker on the bank’s output is what protects the wiring and motor from a short downstream.
References & Sources
- West Marine. “Trolling Motor Battery Wiring Guide.” Covers series wiring logic, jumper gauge matching, and step-by-step battery connection.
- MasterFishingMag. “Wiring a 24 Volt Trolling Motor System.” Provides ABYC-oriented cable sizing, voltage drop limits, and marine breaker specifications.