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Charging lithium on a boat

Full battery every trip, for about $0.23 a charge.

A lithium charger at home, a DC-to-DC charger off the engine, or a solar panel: here is which one you need, what it costs, and the one mistake that shortens a lithium battery's life.
The three waysWhat not to do

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$0.23

To fill a 12V 100Ah lithium

At 18.31¢ a kWh, the US average

2.5 hr

Engine time to refill it

Through a 40 A DC-to-DC charger

32°F

Never charge below this

Battery University

Three ways to charge

1. Plug-in charger at home or the dock

A lithium charger matched to your voltage

The simplest and cheapest way. Redodo sells one for each trolling voltage: 12 V ($59.99), 24 V ($109.99) and 36 V ($155.99). A plug-in lithium charger for one 12 V battery; Redodo says it takes a 12V 50Ah battery to half in 2.5 hours.

  • Charges overnight
  • Lithium voltage built in
$59.99when we checked*See the 12 V charger (opens in a new tab)

2. DC-to-DC charger off the engine

Redodo 12V 40A DC to DC Charger with MPPT

Charges a lithium house or trolling battery from the engine's starting battery while you run, or from solar panels through its built-in MPPT input. It protects a small alternator from a lithium battery's appetite, and charges at the right voltage for lithium, AGM or gel.

  • Flat 12V 100Ah: about 2.5 hours of running
  • Solar input built in
$175.99when we checked*Check price (opens in a new tab)

Also good: Bluetti D40

Bluetti D40 DC-DC battery charger

12 V, up to 30 A into a lithium, AGM or lead-acid battery from the starting battery, solar, or a Bluetti AC200L. A good fit if you already own a Bluetti power station.

  • Up to 30 A
  • Lithium, AGM and lead-acid
$199when we checked*Check price (opens in a new tab)

3. Away from shore power

Bluetti Elite 100 V2 power station

Camping at the lake with no hookup? A 1,024 Wh power station can run a plug-in lithium charger and put back about 68% of a 12V 100Ah battery, then recharge itself from solar panels during the day.

  • About 68% of a 12V 100Ah
  • 25 lb
$499when we checked*Check price (opens in a new tab)

Mistakes that shorten a lithium battery's life

Using a lead-acid charger with desulfation or equalize on. Those modes push the voltage high on purpose. Use a lithium setting, or a charger made for LiFePO4.
Charging below freezing. Lithium must not be charged below 32°F (Battery University). Bring it inside, or buy one that pauses charging or heats itself.
Wiring it straight to the outboard's charging lead.Put a DC-to-DC charger in between so the alternator isn't run flat out for hours.

Myths, answered

"Lithium needs babysitting."Less than lead-acid. There's no water to top up, it doesn't need a full charge after every trip to stay healthy, and the battery's own management system stops it overcharging.
"Charging gear makes lithium too expensive." A lithium charger starts at $59.99. Many marine on-board chargers already have a lithium mode; check yours before buying anything.

Frequently asked questions

Can you charge a lithium battery with a regular battery charger?

Only if it has a lithium (LiFePO4) setting. A charger made for lead-acid can stop short and leave the battery partly empty, and its desulfation or equalize mode can push the voltage too high. Redodo's figures for full charge are 14.4 V for 12 V batteries and 28.8 V for 24 V.

Can you charge a lithium battery with the boat's alternator?

Yes, through a DC-to-DC charger. A lithium battery will pull as much current as the alternator can give, which can overheat a small outboard's charging system. A DC-to-DC charger limits the current and charges at the right voltage: Redodo's 12V 40A unit ($175.99) refills a flat 12V 100Ah lithium in about 2.5 hours of running.

Can you charge a lithium battery with a solar panel on a boat?

Yes, with a solar charge controller set for lithium, or a DC-to-DC charger with a solar input such as Redodo's 40A with MPPT. A panel on a T-top or bimini can keep an electronics battery topped up between trips.

How much does it cost to charge a trolling motor battery?

Very little. Filling a flat 12V 100Ah lithium (1,280 Wh) takes about $0.23 of electricity at the US average price. A whole season of weekend trips costs less than one tank of gas.

Can I charge a lithium battery in the cold?

Not below 32°F (Battery University). Many lithium batteries, including most Redodo trolling batteries, pause charging below freezing and resume at 41°F; self-heating models warm up first and then charge.

Follow your battery, charger and engine makers' wiring instructions and fuse every connection. Prices are copied from makers' US websites on October 20, 2026 and change often. Redodo and Bluetti links are sponsored. See our disclaimer.

Sources

  1. Redodo 12V 40A DC to DC Charger with MPPT — checked October 20, 2026
  2. Redodo 14.6V 10A LiFePO4 Battery Charger — checked October 20, 2026
  3. Redodo 29.2V 20A Mini LiFePO4 Charger (for 24 V) — checked October 20, 2026
  4. Redodo 43.8V 25A Lithium Charger (for 36 V) — checked October 20, 2026
  5. Bluetti D40 DC-DC battery charger — checked October 20, 2026
  6. Bluetti Elite 100 V2 — checked October 19, 2026
  7. Battery University BU-410: Charging at high and low temperatures
  8. EIA average residential electricity price — July 2026

Keep going

Want to charge from the sun at home? See plug-in solar.

Photo: Jackery Power Station on Unsplash (Unsplash License).