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The short answer. Ultrex 80 lb is a 24 V motor, Ultrex 112 lb is 36 V. Minn Kota lists 56 A and 52 A max draw, a 60 A breaker for both, and 8 AWG for the first 5 ft of extension. Lithium is allowed, with a catch: Minn Kota says to avoid long runs above 85% speed on lithium, or the motor can be damaged.
The lithium catch, first
This is the older brushed Ultrex, not the QUEST. Its manual says the motor “can run on Lithium-Ion batteries” but was “specifically designed” for lead-acid. Lithium holds its voltage higher for longer, so the manual warns that running “at speeds higher than 85% for a prolonged period could cause permanent damage to the motor.”
Read that as: lithium is fine, pin it under 85% for long stretches. Short bursts at full speed aren’t what the sentence is about. The manual doesn’t say where 85% sits on the pedal, so watch your speed readout.
Numbers by thrust
| Model | Volts | Max draw | Breaker | Extension at 5 / 10 / 15 / 20 / 25 ft |
|---|---|---|---|---|
| Ultrex 80 | 24 | 56 A | 60 A | 8 / 6 / 6 / 4 / 2 AWG |
| Ultrex 112 | 36 | 52 A | 60 A | 8 / 8 / 8 / 6 / 4 AWG |
The 36 V motor pulls fewer amps for more thrust, which is why its wire stays lighter. Factory leads are 10 AWG. The table counts from the batteries to those leads, assumes 105 C wire and 3% drop, and stops at 25 ft. Beyond that, Minn Kota points you to a marine technician.
Breaker: Minn Kota recommends its MKR-19 60 A. We don’t carry a 60 A breaker yet.
Packs that cover the draw
Minn Kota’s sizing is lead-acid only: 105 Ah or more. For lithium we match voltage and make sure the pack’s continuous discharge rating clears the max draw. That’s our rule, not Minn Kota’s.
For the Ultrex 80 (24 V): – Pro-Guide 24VM90 24V 90Ah lithium, 90 A continuous – Pro-Guide 24VM115 24V 115Ah lithium, 100 A continuous
For the Ultrex 112 (36 V): – Pro-Guide 36VM60 36V 60Ah lithium, 60 A continuous – Pro-Guide 36VM75 36V 75Ah lithium, 75 A continuous
Both 36 V packs clear 52 A. The 24VM90 at 90 A has the most headroom of the four.
Run time, as an example
Lithium math from the Run time calculator trolling mode: 80% of the amp hours, divided by the amps, at room temperature.
| Pack | Motor | Full draw | Half draw |
|---|---|---|---|
| 24VM90 | Ultrex 80, 56 A | 1 h 17 min | 2 h 34 min |
| 24VM115 | Ultrex 80, 56 A | 1 h 39 min | 3 h 17 min |
| 36VM60 | Ultrex 112, 52 A | 55 min | 1 h 51 min |
| 36VM75 | Ultrex 112, 52 A | 1 h 09 min | 2 h 18 min |
Minn Kota says max draw only shows up now and then. Under the 85% ceiling the manual asks for on lithium, you’ll sit nearer the right-hand column most of the day.
Hooking it up
One pack: motor positive through the 60 A breaker to the pack’s positive, negative to negative. Two or three 12 V batteries: series, with the breaker at the last positive. Steps and a diagram are in Trolling motor battery: 12V, 24V or 36V, wired right.
Things the Ultrex manual ties to its warranty: – Chargers (alternator or DC) that join the trolling bank’s negative to the crank battery’s negative. The motor has a bonding wire with a 3 A fuse inside; that tie “can damage” it. – Accessories on the wrong battery. Nothing but the motor on the trolling bank.
There’s no battery meter on an Ultrex. If it loses power after a short run, Minn Kota’s troubleshooting says check the charge and restore it to full.
Charging
Pull the motor plug before you charge. Use a multi-stage charger set for lithium at the pack maker’s voltage: 28.8 V for Pro-Guide 24 V, 43.2 V for 36 V. We don’t list a 24 V or 36 V lithium charger yet; our shore charger is a 12 V unit, which only helps if you run 12 V batteries in series, one bank each.
Quick answers
Can the Ultrex run on a lithium battery? Yes, per Minn Kota, as long as you keep prolonged running under 85% speed.
Ultrex 112: how many batteries? Three 12 V in series, or one 36 V pack.
What breaker does an Ultrex 80 need? 60 A, manual reset. Minn Kota recommends the MKR-19.
Does cold matter? The motor’s rated range is -10 C to 50 C. Lithium packs have their own charge temperature limits; check the pack’s sheet.
Sources
- Minn Kota Ultrex owner’s manual 2297162 (Rev K, 09/25), pages 6, 48-51, 67, 70-71, 76, 79
- Minn Kota Ultrex product page: https://minnkota.johnsonoutdoors.com/us/shop/freshwater-trolling-motors/ultrex
- Pro-Guide brochures and product pages (our 24VM90, 24VM115, 36VM60, 36VM75 pages)
- Trolling motor battery: 12V, 24V or 36V, wired right, Run time calculator, Wire gauge calculator
