How Much Trolling Motor and Battery Does Your Boat Need?
A trolling motor, its batteries, the wire, the breaker and the charger are one electrical system. Enter your boat and your fishing day, and the planner sizes all of it from Minn Kota's published sizing table and standard battery math.
How the planner works
Every step below is either a published manufacturer figure or a formula stated in full. Where the planner uses a rule of thumb rather than a published number, it says so.
1. Loaded weight and thrust
Minimum thrust = loaded weight / 100 x 2 lb. This is Minn Kota's guidance: at least 2 lb of thrust per 100 lb of fully loaded boat. Loaded weight is hull + outboard and fuel + people + gear + the trolling batteries themselves, which the planner adds from a typical weight per amp-hour for the chemistry you pick (flooded 0.6, AGM 0.65, LiFePO4 0.27 lb per Ah; a site estimate, so check your battery's spec sheet). It then multiplies by a conditions margin, a site rule of thumb: calm water x1.00, moderate wind or current x1.25, strong wind, river current or tide x1.50. The result rounds up to the next motor size sold: 30, 40, 45 or 55 lb at 12 V, 70 or 80 lb at 24 V, 101 or 112 lb at 36 V.
2. Voltage, batteries and current
Voltage follows the thrust class, and each 12 V is one battery in series. Minn Kota requires the batteries in a series bank to be the same make, type, size and age, with jumpers one wire size larger than the motor leads. A second string in parallel doubles the amp-hours at the same voltage. Average current at part throttle uses I = Imax x t1.5, where Imax is the table's maximum draw and t is the fraction of full thrust. This comes from propeller momentum theory (the power needed rises with thrust to the 1.5 power) and fits variable-speed (PWM) motors. It is a model, not a measurement: older 5-speed motors with resistor speed control draw more at low settings than it predicts, and Minn Kota notes that its maximum figures are intermittent, not continuous ratings.
3. Runtime and the battery you need
Runtime = Ceff x usable fraction / current. The effective capacity uses Peukert's law, Ceff = C20 x (C20 / (20 x I))k-1, capped at the rated capacity, with typical exponents k = 1.2 for flooded, 1.1 for AGM and 1.05 for LiFePO4. The usable fraction is 50% for lead-acid (the depth of discharge that protects cycle life) and 80% for LiFePO4 (staying clear of typical battery-management cut-offs). Both are typical values, not a specific product's. The amp-hours you need are found by solving the same equation for C20.
| Minn Kota run-time grade | Voltage | Group size | Amp-hours |
|---|---|---|---|
| Good | 12 | 24 | 70-85 |
| Better | 12 | 27 | 85-110 |
| Best | 12 | 31 | 95-125 |
Minn Kota recommends a deep-cycle marine battery of at least 110 Ah, and a separate trolling battery rather than the outboard's cranking battery. The planner suggests the smallest lead-acid group whose range covers your need. The battery types guide explains deep-cycle versus starting batteries.
4. Wire gauge and breaker
A direct lookup in Minn Kota's Conductor Gauge and Circuit Breaker Sizing Table (Rev. 8.17.2021) by thrust and extension length, rounded up to the next listed length. Extension length is the distance from the batteries to the motor leads. The table assumes no more than 2 conductors bundled together, 105 C rated insulation and no more than 5% voltage drop at full power. The percentage in each cell below is our own check: maximum draw x copper resistance at 20 C for the round trip, divided by system voltage. Every cell lands at 5.0% or less, which is how the table was built.
| Motor | Max draw | Breaker | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft |
|---|---|---|---|---|---|---|---|
| 30 lb | 30 A | 50 A @ 12 V | 10 AWG 2.5% | 10 AWG 5.0% | 8 AWG 4.7% | 6 AWG 4.0% | 4 AWG 3.1% |
| 40 / 45 lb | 42 A | 50 A @ 12 V | 10 AWG 3.5% | 8 AWG 4.4% | 6 AWG 4.1% | 4 AWG 3.5% | 4 AWG 4.3% |
| 50 / 55 lb | 50 A | 60 A @ 12 V | 8 AWG 2.6% | 6 AWG 3.3% | 4 AWG 3.1% | 4 AWG 4.1% | 2 AWG 3.3% |
| 70 lb | 42 A | 50 A @ 24 V | 10 AWG 1.7% | 10 AWG 3.5% | 8 AWG 3.3% | 8 AWG 4.4% | 6 AWG 3.5% |
| 80 lb | 56 A | 60 A @ 24 V | 8 AWG 1.5% | 8 AWG 2.9% | 8 AWG 4.4% | 6 AWG 3.7% | 6 AWG 4.6% |
| 101 lb | 46 A | 50 A @ 36 V | 8 AWG 0.8% | 8 AWG 1.6% | 8 AWG 2.4% | 8 AWG 3.2% | 8 AWG 4.0% |
| 112 lb | 52 A | 60 A @ 36 V | 8 AWG 0.9% | 8 AWG 1.8% | 8 AWG 2.7% | 8 AWG 3.6% | 8 AWG 4.5% |
Copper resistance per 1,000 ft at 20 C: 10 AWG 0.9989 ohm (5.3 mm²), 8 AWG 0.6282 ohm (8.4 mm²), 6 AWG 0.3951 ohm (13.3 mm²), 4 AWG 0.2485 ohm (21.2 mm²), 2 AWG 0.1563 ohm (33.6 mm²). Every ungrounded conductor needs a manually reset, trip-free circuit breaker or fuse (the sheet cites 33 CFR 183 and ABYC E-11). Wiring changes belong with a qualified marine technician when you are unsure; see the wiring guide.
5. Charger
Amps per bank = amp-hours used per battery / hours until the next trip x 1.2 for lead-acid (1.05 for LiFePO4), rounded up to a common size of 5, 10, 15 or 20 A per bank. The factor covers charging losses and is a typical value. One bank per battery. Minn Kota warns that failing to recharge lead-acid within 12 to 24 hours is the leading cause of early battery failure. The charger guide covers onboard versus portable units.
6. Fish finder battery
Amp-hours = draw x hours on the water / usable fraction, with the same Peukert correction. A small display draws around an amp; check your unit's spec sheet, because a large display plus a forward-facing sonar module draws several times that (see forward-facing sonar).
Source: Minn Kota, "Battery & Wiring Installation", Johnson Outdoors Marine Electronics, Rev. 8.17.2021, read October 2026. Not affiliated with Minn Kota or Johnson Outdoors. Choosing between motor styles? Read bow mount vs transom mount.
Frequently asked questions
Quick answers to what anglers ask us most
How much thrust does my boat need?
Minn Kota’s rule is at least 2 lb of thrust for every 100 lb of fully loaded boat: hull, outboard, fuel, batteries, people and gear. A 1,500 lb loaded boat needs at least 30 lb. The planner then adds a margin for wind and current (25% for moderate conditions, 50% for strong wind, river current or tide) and rounds up to the next motor size sold. Thrust is cheap compared with fighting wind all day on an undersized motor.
Should I pick a 12 V, 24 V or 36 V trolling motor?
In the Minn Kota lineup the voltage follows the thrust: 12 V motors go up to 55 lb, 24 V covers 70 and 80 lb, and 36 V covers 101 and 112 lb. Each 12 V of system voltage is one more battery in series, so a 36 V motor needs three identical batteries. Higher voltage moves more power through the same wire with less current, which is why the 36 V rows of the table stay at 8 AWG out to 25 ft. The voltage guide covers the trade-off in detail.
How long will a 100 Ah battery run a trolling motor?
It depends on the current, and current climbs steeply with speed. A 55 lb motor (50 A maximum on Minn Kota’s table) averages about 17.7 A at half thrust under the planner’s model. One 100 Ah AGM battery, used down to 50% to protect its life, gives about 2.5 hours at that draw. A 100 Ah LiFePO4 battery, used to 80%, gives about 4.2 hours. At full throttle every figure drops sharply. The trolling motor battery guide works through more cases.
What wire size and circuit breaker does a trolling motor need?
Use the manufacturer’s table for your motor and the distance from the batteries to the motor leads. On Minn Kota’s table a 55 lb motor with a 15 ft extension needs 4 AWG wire and a 60 A breaker, while an 80 lb 24 V motor at the same distance needs only 8 AWG. Every ungrounded conductor needs a manually reset, trip-free breaker or fuse. Above 25 ft, Minn Kota recommends a qualified marine technician. The wiring guide covers plugs and terminals.
Can my fish finder run off the trolling motor battery?
On a 12 V system it can, and the planner adds its draw to the bank if you choose that. It is not the recommended setup: in a 24 V or 36 V bank, tapping one battery drains it faster than the others and unbalances the string, and a separate small battery keeps the motor’s electrical noise off the sonar supply. The planner sizes that separate battery from the finder’s draw and your hours on the water.
Is a lithium battery worth it for a trolling motor?
The planner shows the trade in numbers: for the same day on the water, a LiFePO4 bank needs fewer rated amp-hours (you can use about 80% of it instead of 50%) and the bank weighs well under half as much. It costs more up front and needs a charger with a lithium profile. Whether that is worth it depends on how hard you run the motor and how much weight your boat can carry. See lithium vs AGM.
Why is the runtime lower than amp-hours divided by amps?
Two reasons. You should not drain a lead-acid battery past about half its capacity if you want it to last, so only 50% counts (80% for LiFePO4). And a battery’s rating is measured over 20 hours; at the higher currents a trolling motor pulls, lead-acid delivers less than its label (the Peukert effect). The planner applies both and never credits more than the rated capacity.
Does this work for MotorGuide, Garmin or Lowrance motors?
The thrust rule, the battery math and the voltage logic apply to any brushed or brushless trolling motor. The amp draw, breaker and wire columns come from Minn Kota’s published table, so for another brand check its manual: if its maximum draw or required breaker differs, the manual wins. The planner covers small-boat motors up to 112 lb and 36 V.