Key points at a glance Key points at a glance. Original editorial diagram. The trolling motor ran all morning. That evening the charger sat there and did nothing.
Quick answer: A cold lithium (LiFePO4) trolling battery can run your motor and still refuse a charge, because makers set separate limits for discharging and charging, and charging a cold cell can damage it. Victron's Lithium NG, for example, only charges between +5°C (41°F) and +50°C (122°F). Check your battery's manual, and call us if the charger and battery won't agree.
Key points at a glance. Original editorial diagram.
The trolling motor ran all morning. That evening the charger sat there and did nothing.
If you've moved to a lithium iron phosphate battery (LiFePO4 on the label), this is the cold-weather surprise nobody mentions at the checkout. The battery that happily spins your motor at dawn may not want to take a charge while the same cold is still in its cells. Both things can be true at once, and neither one means the battery is dead.
On Rice Lake, fall walleye and crappie trolling runs right into the cold weeks, which is exactly when this shows up. This post is about trolling-motor banks. Starting an outboard is a different job, and our Mercury boat battery guide covers that side.
Why Will It Run the Motor but Not Take a Charge?
For a LiFePO4 battery, the temperatures where it can deliver power aren't the same as the temperatures where it can accept a charge. Battle Born explains that its batteries can discharge in cold conditions, while charging at low temperatures can damage the cells.
So a battery can run your motor and a charger can refuse to start in the same hour. That isn't a fault. The protection is doing its job, and forcing a charge through a cold lithium cell is the one thing you're trying to avoid.
Don't Treat 0°C as the Magic Line
You've probably heard that lithium batteries shouldn't charge below freezing. It's a good warning, but it isn't a charging instruction.
Victron's Lithium NG 12.8V manual is a good example of how specific the real numbers get:
| Victron Lithium NG 12.8V |
Manual limit |
| Charging allowed |
+5°C to +50°C (41°F to 122°F) |
| Charge current below 15°C (59°F) |
Reduced to a maximum of 0.3C |
| Discharging allowed |
-20°C to +50°C (-4°F to 122°F) |
That 0.3C figure means 30 amps on a 100 Ah battery. A charger that pushes more than that into a cool battery is outside Victron's instructions, even on a day well above freezing. These numbers belong to that battery family, so treat them as an example, not settings for your brand.
The takeaway: a day a few degrees above zero can still be too cold to charge. Start with the model number on your battery and its current manual, and look for separate entries for charging, discharging and storage. If a product page gives one broad operating range, it hasn't answered all three questions.
The Battery's Temperature Is What Counts
The weather app tells you about the air. A battery's protection system responds to the temperature inside the battery.
Battle Born says its integrated heating responds to internal battery temperature. On its heated models, the system warms the cells before normal charging starts. Its standard models don't have that heating. "Lithium" on the label won't tell you whether your battery is heated.
A battery that sat overnight on the trailer at 2°C (36°F) doesn't warm up because the afternoon hit 10°C (50°F). If your battery or charger shows a temperature reading, a status message or a cold-charge indicator, use the manual to read it.
The Charger Is Half of the Compatibility Check
A "lithium" setting on a charger is only a start. It needs a battery model and a bank layout beside it.
Minn Kota's support page for its PCL chargers tells owners to check the battery's permitted charging current and voltage against the charger's output. It also says those chargers aren't compatible with single 24V or 36V lithium batteries. A multi-bank charger isn't a universal answer for every trolling-motor setup.
Before you swap a battery or reuse an old charger, put the battery and charger instructions side by side. Count the batteries, note the voltage, and write down how they're wired together. List every charging source in the boat, including anything that charges from the outboard.
Common Mistakes With Cold Lithium Charging
- Reading the forecast instead of the battery. Air temperature and cell temperature aren't the same thing on a cold morning.
- Assuming the BMS handles everything. Victron requires a battery-management system on its NG battery and tells installers to make sure chargers switch off at the minimum temperature limit, ideally under BMS control. That's an installation job, not something the label promises.
- Forcing it. Don't bypass a temperature-related stop or flip charger modes to get a charge in. Follow the maker's fault guidance, and if the cause still isn't clear, bring the model details to us.
- Reusing the old charger without checking. Match its output to the battery's permitted current and voltage first.
What We See at HBW
Rice Lake fall trolling sets up the problem neatly. The boat sits overnight at the dock or on the trailer, the battery cools right down with it, and the next recharge happens in a cold garage or a cold boat. That's when a lithium bank and an older charger stop agreeing.
The most useful thing you can do is arrive with the information: battery model, charger model, how the banks are wired, and the manual pages that cover charging temperature. With those in hand, we can sort out whether you have a settings question or an equipment question. If you troll from a Mercury ProKicker rig, the ProKicker fishing guide covers the outboard side of that setup.
For boats we store, batteries are disconnected and left in the boat, then checked and charged as required in the fall and again in the spring. Our winter storage near Toronto page explains how storage works here.
Keep One Equipment Note
Save the battery model, the charger model and the manual pages in one place, on your phone or in the glovebox. Write down the answers to these four questions:
- What battery temperature permits charging, and are there current limits inside that range?
- How does this installation stop charging outside the permitted conditions?
- Is heating actually fitted, and what does its maker require?
- Is this charger and bank arrangement approved for these batteries?
For the off-season, use the battery maker's own storage guidance. A cold-charge warning isn't a storage rule.
The motor running yesterday tells you the battery had power yesterday. The next recharge needs its own answer.
Sources
Got a Battery and a Charger That Won't Agree?
Bring us the battery model, the charger model and how the banks are wired. We'll sort out whether it's settings, compatibility or something that needs a closer look. Put in a service request at hbwservice.ca and drop the boat off, or call us first.
Phone: 905-342-2153
Service: hbwservice.ca
Configurator: mercuryrepower.ca
Address: 5369 Harris Boat Works Rd, Gores Landing, ON
