Bigger trolling motors run on 24 or 36 volts by joining 12-volt batteries in series. Here is how that is wired, where the circuit breaker goes, and what wire size the motor makers call for at each length of run.
A 12-volt motor runs from one 12-volt deep cycle battery. A 24-volt motor needs two 12-volt batteries wired in series, and a 36-volt motor needs three. Minn Kota says the batteries in a series bank must be the same make, type, size and age.
Minn Kota recommends separate deep cycle batteries for the trolling motor if you use a cranking battery to start a gas outboard, and a deep cycle marine battery of at least 110 amp-hours for best results.
Make sure the trolling motor is unplugged. Garmin says the circuit breaker must be in the off position before you connect the motor's power cables.
Connect a jumper cable from battery 1's positive terminal to battery 2's negative terminal. Minn Kota says the jumper should be one wire size larger than the motor's lead wire.
Put a manual reset circuit breaker in the positive lead, as close to the battery as you can. ABYC E-11 calls for overcurrent protection within 7 inches of the battery, or up to 72 inches when the wire runs in a sheath and connects directly to a battery terminal; MotorGuide's "within 6 feet" matches that outer limit. Minn Kota points out that Coast Guard rules require every ungrounded current-carrying conductor to be protected by a manually reset, trip-free circuit breaker or a fuse.
Run the motor's red positive lead, through the breaker, to battery 2's positive terminal. Connect the black negative lead to battery 1's negative terminal.
Minn Kota says to keep all battery post connections tight. MotorGuide secures its battery cables with nylock nuts, because wing nuts can work loose.
Minn Kota warns that improper wiring of a 24 or 36-volt system could cause a battery explosion, so check every connection against the diagram. Don't switch the motor on until the propeller is in the water.
Add a third battery. Minn Kota's sequence: jumper battery 1 positive to battery 2 negative, and battery 2 positive to battery 3 negative, each jumper one size larger than the motor lead. The motor's positive lead goes, through the breaker, to battery 3 positive, and its negative lead to battery 1 negative.
From Minn Kota's conductor gauge and circuit breaker sizing table. Length is the extension from the batteries to the motor's leads.
| Motor thrust | Breaker | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft |
|---|---|---|---|---|---|---|
| 30 lb (12 V) | 50 A | 10 AWG | 10 AWG | 8 AWG | 6 AWG | 4 AWG |
| 40 or 45 lb (12 V) | 50 A | 10 AWG | 8 AWG | 6 AWG | 4 AWG | 4 AWG |
| 50 or 55 lb (12 V) | 60 A | 8 AWG | 6 AWG | 4 AWG | 4 AWG | 2 AWG |
| 70 lb (24 V) | 50 A | 10 AWG | 10 AWG | 8 AWG | 8 AWG | 6 AWG |
| 80 lb (24 V) | 60 A | 8 AWG | 8 AWG | 8 AWG | 6 AWG | 6 AWG |
| 101 lb (36 V) | 50 A | 8 AWG | 8 AWG | 8 AWG | 8 AWG | 8 AWG |
| 112 lb (36 V) | 60 A | 8 AWG | 8 AWG | 8 AWG | 8 AWG | 8 AWG |
Each maker publishes its own figures; use the ones for your motor. Garmin requires a circuit breaker rated for 60 amps continuous for its Force motor, on a 24 or 36-volt bank that can supply 60 amps continuously. For extending its power cable it lists 6 AWG up to 10 feet, and 6 AWG minimum with 4 AWG optimal from 10 to 20 feet and 2 AWG optimal from 20 to 30 feet.
MotorGuide's X5 manual says not to extend the included 10-gauge cables by more than 6 feet, for 10 feet in total, and to use its 8-gauge cables for longer runs.
A plug and receptacle where the cable enters the boat lets you disconnect the motor easily. Garmin calls for one rated at 60 amps or more for its Force. Minn Kota says to observe proper polarity when installing a lead wire plug and to follow your boat owner's manual.
Minn Kota, Battery & Wiring Installation (Rev. 8.17.2021); MotorGuide, X5 Owner's Manual (2017); Garmin, Force Trolling Motor Installation Instructions; ABYC E-11, as excerpted by Paneltronics.