What Size Battery for a Trolling Motor?

What size battery for a trolling motor? Start with voltage, because the motor decides it: a 12-volt motor runs on one 12-volt battery, a 24-volt motor on two 12-volt batteries connected in series, and a 36-volt motor on three. Then choose the amp-hour (Ah) capacity, which sets how long you can run, and finally the group size, which is the physical case that has to fit your battery box or compartment. Choosing lithium instead of lead-acid changes how many of those amp-hours you can actually use and how much the battery weighs.

This guide is general product information, not repair or electrical safety advice. Follow the installation, wiring, and charging instructions in your product’s manual, stop using any battery, charger, or electronics that overheat, swell, or smell of burning, and contact the manufacturer.

The steps below use what motor makers Newport and Garmin publish about power, plus guidance from two battery makers, each linked where cited. Battery makers sell the batteries they describe, so read their figures as planning numbers, and treat your motor’s manual as the final word.

Step 1: Match the Battery Voltage to the Motor

Voltage is not a choice you make on the battery side. It comes from the motor’s specifications, and makers state it plainly:

• Newport’s trolling motor FAQ says its 36, 46, 55, and 62 lb thrust motors run on one 12-volt battery, and its 86 lb motor runs on two 12-volt batteries connected in series.
• Newport’s buyer’s guide says the amount of thrust determines the battery setup each motor needs, and that its 112 lb motors require three 12-volt marine batteries.
• Garmin’s Force installation instructions require a 24 or 36 volt battery bank capable of supplying 60 A continuously. The Force owner’s manual lists the input voltage as 20 to 45 Vdc, so a single 12-volt battery is outside its range.

Some motors accept more than one voltage, and the choice changes the output. Garmin’s guide to choosing a trolling motor says the Force Current kayak motor delivers 30 lb of thrust on 12-volt power or 50 lb on 24-volt power. If you are still matching thrust to your boat, settle that first, since picking the motor is what sets the voltage.

How the batteries connect is a job for the manual. Newport’s Kayak Series owner’s manual shows separate diagrams for a single battery, two batteries in parallel at 12 volts, and two batteries in series for the 24-volt 86 lb model, each recommending a circuit breaker on the positive wire. For safety, follow the diagram in your own motor’s manual, or have a qualified marine technician wire the bank. The Kayak Series manual gives no breaker rating, and Newport’s own pages give two: its trolling motor FAQ says the 86 lb motor is “rated for 50A” and recommends a 50 amp breaker for the 46, 55, and 86 lb motors, while its NV Series product page lists 60A for the 55, 62, and 86 lb versions. Go by the label or paperwork that came with your motor, or ask Newport which rating applies. The same manual warns that a charging battery gives off hydrogen and oxygen gases and that sparks or flames nearby can cause an explosion.

Step 2: Use a Deep-Cycle Battery, Not a Starting Battery

Battery type matters before size. Newport’s manual recommends a deep cycle or marine battery, saying they last much longer and are designed for this use. LiTime, a lithium battery maker, explains the difference in its guide to trolling motor battery size and type: a deep-cycle battery is designed to provide steady power over long periods and withstand repeated deep discharges, while a starting (cranking) battery delivers a short burst of high current to start an outboard. LiTime says a starting battery should not be the primary power source for a trolling motor. The battery under the hood of your truck is the wrong tool here, whatever its size.

Step 3: Choose the Amp-Hour Capacity

Amp-hours are the “size” most anglers mean. Newport’s FAQ recommends a 12-volt deep cycle or marine battery rated for 50 Ah or greater for its 12-volt motors, which works as a floor. Above that floor, the trade-off is time on the water against weight. LiTime puts it this way: higher capacity batteries offer longer run times but are heavier and more expensive. It describes a 12-volt 100Ah battery as suitable for most half-day or mixed-speed fishing trips, and suggests adding a 20% safety margin for high winds, strong currents, or heavy throttle use.

The speed you actually fish at drives the number more than the motor’s rating. Garmin’s Force owner’s manual publishes current draw by throttle level: on a 36-volt supply, it lists about 10 A at 50% throttle and 54 A at 100%. An angler who spends the day creeping a shoreline at low settings needs far fewer amp-hours than one who holds a heavy boat against the wind at high settings. The step-by-step run-time math, with worked examples, is in the guide on how long a 12 volt trolling motor lasts on one charge.

One detail trips people up with 24 and 36 volt systems. Connecting batteries in series adds their voltage, but the bank’s amp-hour rating stays that of one battery. Two 100Ah 12-volt batteries in series make a 24-volt bank rated at 100Ah, not 200Ah, so choose the capacity of each battery with that in mind.

Step 4: Check the Group Size Against Your Battery Box

Group size is mainly about fit. Battle Born Batteries explains in its article on what a Group 24 battery is that group size refers to a battery’s physical characteristics, such as size, capacity, and terminal location, and that the traditional sizes come from Battery Council International, which represents the lead-acid industry. It lists a Group 24 battery at about 10.5 x 6.2 x 8.9 in, names powering a kayak trolling motor as a popular use, and notes that lithium batteries are often not labeled by group size, so you have to check their dimensions yourself. That 10.5 x 6.2 x 8.9 in figure is Battle Born’s own measurement; Battery Council International’s group size chart lists only maximum overall dimensions for each group, so compare the exact model’s published size with your battery tray.

LiTime’s sizing guide describes the three sizes most often discussed for trolling motors:

• Group 24: compact, suited to smaller boats, lighter loads, and limited battery compartments.
• Group 27: a mid-size option with more capacity than Group 24.
• Group 31: a larger format commonly chosen for heavier loads, longer run times, and demanding marine use.

Before you buy, measure the battery box or compartment, including the height under any lid, and note which side the terminals need to sit on for your cables to reach. On a bass boat, check whether the compartment holds two or three batteries side by side, since a 36-volt motor needs room for three. On a kayak, the bigger question is weight and where it sits in the hull.

Lead-Acid or Lithium: How Chemistry Changes the Size

The same amp-hour label does not mean the same usable energy. In its guide to how long trolling motor batteries last, LiTime says users commonly plan on about 40 to 50 Ah from a 100Ah lead-acid battery, to avoid routine deep discharge, and about 80 to 90 Ah from a 100Ah LiFePO4 (lithium iron phosphate) battery while keeping a practical reserve. LiTime calls these planning examples rather than guaranteed specifications. By those figures, a 100Ah lithium battery plans out to about as much usable capacity as roughly 200Ah of lead-acid, which is why lithium buyers often choose a lower Ah rating.

Weight follows the same pattern. LiTime describes lithium as lower in weight than comparable lead-acid capacity, and calls flooded lead-acid batteries affordable and widely available but heavy and maintenance-intensive. On a kayak or a small jon boat, that weight difference can matter as much as run time.

Check what your motor maker says before switching chemistry. Newport’s FAQ states that it prefers lead-acid over lithium, and its Kayak Series manual says the motor’s battery meter is designed for 12-volt deep cycle batteries and cannot be trusted on a lithium battery. Garmin’s Force manual says the motor’s battery level indicators are optimized for lead-acid and may be inaccurate for other types such as lithium-ion. Lithium also needs a compatible charger, according to LiTime, so plan for that if your boat has an onboard charger set up for lead-acid. How many years each battery type lasts is a separate question, with its own figures from battery makers.

What Size Battery for a Trolling Motor: Three Common Setups

• Kayak with a 12-volt motor: one 12-volt deep-cycle battery, at least the 50 Ah floor Newport recommends for its 12-volt motors, in a case that fits the kayak’s mount or hatch. Lithium saves weight here if the motor maker supports it.
• Jon boat with a 24-volt motor: two 12-volt deep-cycle batteries connected in series as the motor’s manual shows, such as Newport’s 86 lb model. Size each battery for the run time you want, since the series bank keeps one battery’s Ah rating.
• 18 ft bass boat with a 36-volt bow mount: three 12-volt batteries forming a 36-volt bank. For the Garmin Force, the bank must be able to supply 60 A continuously, per the installation instructions, and the compartment has to hold all three.

Bigger isn’t for everyone. A larger battery adds weight to a boat that may already be close to its maximum load, and on a light kayak or canoe it can change how the hull sits in the water. If you fish short sessions on calm water at low speeds, you can skip the jump to a larger case and stay near the floor your motor maker recommends.

Frequently Asked Questions

What size battery do I need for a 55 lb trolling motor?

For Newport’s 55 lb motors, one 12-volt battery: the FAQ lists that thrust as a single-battery, 12-volt motor and recommends a deep cycle or marine battery rated for 50 Ah or greater. Other brands’ 55 lb motors may differ, so confirm the voltage in your manual, then add capacity for longer days or windy water.

What size lithium battery for a trolling motor?

The same voltage as the motor requires, with an Ah rating chosen for usable capacity. By LiTime’s planning figures, a lithium battery delivers more of its rating than lead-acid, so a lower Ah lithium battery can match a larger lead-acid one. Check first that your motor maker supports lithium, that its battery meter reads it correctly, and that your charger is compatible.

What type of battery does a trolling motor need?

A deep-cycle battery in the voltage the motor requires. LiTime describes a deep-cycle battery as built for steady power over long periods and repeated deep discharges, and says a starting battery should not be the primary power source for a trolling motor. Among deep-cycle batteries, LiTime compares flooded lead-acid, AGM, and lithium iron phosphate (LiFePO4), which differ mainly in cost, weight, lifespan, usable capacity, and maintenance. The motor maker decides which of those it supports: Newport’s battery recommendations say all of its trolling motors require a marine deep-cycle AGM, gel, or lead-acid battery, and that lithium can be used but Newport does not recommend it because of an incompatibility with the LED battery meters on its motors. Check your own motor’s manual before you buy.

Can I use a car battery for a trolling motor?

Not as the main power source. A car battery is a starting battery, built for short bursts of high current, and LiTime says a starting battery is not designed for repeated deep discharge and should not be used as the primary power source for a trolling motor.

Can I add a second battery to a 12-volt motor?

Newport’s manual says a larger capacity or an additional battery can be used to extend running time, and it shows a two-battery parallel connection for its 12-volt motors. Use your own motor’s diagram and circuit protection, or have a qualified marine technician do the wiring.

For more on power for small boats, browse the Batteries & Power section; motors are in the Trolling Motors section, and the scoring method is on How We Review.

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