Laying Up a Lithium Boat for a New England Winter

Lithium batteries are far more forgiving over the winter than lead-acid. They don't sulfate, they don't freeze and crack, and they lose only a few percent a month sitting still. That is exactly why owners neglect them. The lithium banks we see damaged over a New England winter almost never fail from the cold. They fail because something on the boat quietly drained them flat between November and April.

There is a second surprise. Ask battery manufacturers how full a lithium bank should be for winter storage and you get different answers, sometimes even within one company's own paperwork. We went through the current documentation from the brands we install most, Epoch, Victron Energy, MG Energy and Mastervolt, so you can lay up your boat the way your battery maker actually specifies.

The Short Version: What Every Manufacturer Agrees On

• Never store it empty. A lithium battery left in low-voltage protection keeps self-discharging, and cells that sit too low can be permanently damaged or refuse to recover.
• Don't park it at 100% for months, especially somewhere warm. Lithium batteries age just by sitting, and they age fastest when held full and hot. That is calendar aging, and it is why most storage targets land in the middle.
• Kill the parasitic loads and physically disconnect. Alarms, stereo memory, chargers, relays, network power and even the BMS itself draw current all winter. A battery switch, pulled fuse or open disconnect beats any software off button.
• Don't charge a cold battery. Charging LiFePO4 below freezing plates lithium onto the anode and causes permanent damage. Unless the battery has a heater, wait until the cells are at 41°F (5°C) or warmer.
• Self-discharge is not the problem. Victron, Epoch and Mastervolt rate their batteries at roughly 3 to 5 percent a month. Loads are the problem.
• Fully charge in the spring so the BMS can balance the cells and resynchronize the state of charge before the first trip.

Why the Storage Charge Matters: Calendar Aging

Every lithium battery loses capacity two ways. Cycle aging comes from use: charging and discharging. Calendar aging happens with the battery doing nothing at all. A bank sitting on a trailer from November to April is aging the whole time, and two things set how fast:

• State of charge. Calendar aging research on LiFePO4 cells shows they fade faster when held at high charge. Every cell sits at a slightly higher internal stress when full, and over months that adds up.
• Temperature. Heat speeds it up far more than cold. Lab storage tests show LiFePO4 cells fading much faster at 113°F (45°C) than at 86°F (30°C). A cold, unheated New England storage building is actually kind to a resting lithium battery, as long as nobody tries to charge it.

So the ideal is a cool place at a middle state of charge. The catch is that a battery stored too low has no margin for self-discharge or a load you missed. That trade-off is why the manufacturers' numbers differ: each is weighing calendar aging against the risk of the battery running flat.

Keep this in proportion. LiFePO4 is the most tolerant lithium chemistry, and one winter at the wrong charge costs a small amount of capacity. One winter run flat by a hidden load can cost the battery.

Step 1: Set the Storage Charge

Our rule of thumb: target 60 percent when your battery manufacturer's guidance permits it. Sixty percent is low enough to slow calendar aging and high enough to leave margin for self-discharge and the load you didn't find. It sits inside MG Energy's 50 to 80 percent range, at the top of Victron's 40 to 60 percent, and within Epoch's guidance for its families rated at 50 percent or higher. It does not fit Mastervolt, which asks for more than 80 percent, or Epoch's 48V 125Ah Essential, which asks for 30 to 50 percent. When the manual says something different, the manual wins.

Why Victron has two answers. The 40 to 60 percent figure is for storing the battery itself, which is exactly what calendar aging favors. The near-full guidance in the battery manuals covers a complete system left unattended, where loads and BMS draw are the bigger threat and the extra charge buys time. If you have truly isolated the bank and will check it, the 40 to 60 percent target is the one to use.

Why Mastervolt is the exception. Mastervolt prioritizes margin: a fuller battery survives a longer stretch of self-discharge and network draw before anyone checks it. If you own an MLI Ultra, follow Mastervolt, not the 60 percent rule.

Epoch revised its own guidance in October 2026, moving from 50 to 80 percent down to about 50 percent for most models, and some Epoch families (golf cart kits, the 48V 125Ah) have their own targets.

How to tell where you are. LiFePO4 voltage is nearly flat between about 20 and 80 percent, so a voltmeter can't tell 50 percent from 70 percent. Use the battery's app or a battery monitor with a shunt, such as the MG Energy Monitor or a Victron SmartShunt. To bring a full battery down to storage level, run the boat's normal loads with the chargers off until the monitor reads the target.

Step 2: Find Every Load and Disconnect It

This step matters more than the storage charge. Epoch works the numbers on a single 90 mA alarm: it empties a half-charged 100Ah battery in about three weeks. On self-discharge alone, the same battery would last more than a year.

The quick math: milliamps x 0.024 = amp-hours lost per day. Common winter drains on boats include:

• Bilge and high-water alarms, CO detectors and security trackers
• Stereo memory, chartplotters and radios wired ahead of the battery switch
• Inverters left in standby instead of off
• Back current from battery chargers, solar charge controllers and DC-DC chargers
• Network power, such as Mastervolt MasterBus set to Always On
• The BMS itself. Victron and MG both call this out, and MG's own module BMS draws a small amount even when not connected to the Master.

Turn off every charge source first (shore power, solar breaker, DC-DC charger), then the inverter and loads, then open the main disconnect. If the battery has a power, storage or lock-off control, use it. Victron notes that switching its SuperPack NG off from the app keeps Bluetooth running and is not suitable for long-term storage; the push button is. On a Mastervolt MLI Ultra, the safety relay knob goes to LOCK OFF.

Not sure what is still drawing current? A battery monitor with a shunt will show it, and it is the first thing we check during a layup.

Step 3: Respect the Cold When Charging

A lithium battery can sit through a New England winter. What it can't do is take a charge in the cold. The documented limits:

The safe rule for any brand: don't charge a non-heated lithium battery below 41°F. That rules out leaving a lead-acid style trickle charger or an unregulated solar panel on a boat in an unheated yard. A properly configured system that blocks cold charging can stay connected; most can't, and should be switched off.

Heated batteries are not heated storage. Epoch documents its heaters as running only while a charger is supplying current, so the cells can accept a charge. They don't keep a stored battery warm. Some batteries, like Victron's SuperPack NG, offer a mode that powers the heater from the battery itself, which spends stored energy all winter. Know which one you have before you rely on it.

Step 4: Decide Where the Battery Spends the Winter

• On a trailer or stands, shrink-wrapped. Set the storage charge, disconnect, and leave an access panel in the wrap so you can check the battery mid-winter. Removing drop-in batteries to a basement is the simplest option if they are easy to get out.
• Still in the water. The bilge pump has to stay powered. Keep it on its own battery and charger that can recharge in freezing weather, and never isolate that circuit. A high-water alarm with remote alerts is cheap insurance.
• Larger systems with a central BMS (MG Master LV, Victron Lynx Smart BMS, Mastervolt MasterBus systems). Follow the BMS manual for isolating the bank from the controller, not just turning the system off.

Step 5: Check It Over the Winter

Put a reminder on the calendar. Victron's data sheets say to check monthly; Epoch says at least every 3 months; Mastervolt recommends recharging every 100 days. Read the state of charge from the app or monitor. If it has dropped noticeably, something is still connected. To top up, let the battery reach 41°F first (never warm it with a heater), charge back to storage level, then disconnect again.

Step 6: Spring Recommissioning

1. Inspect the batteries and connections for corrosion, damage or water.
2. Reconnect with every charger and load off, then close the disconnect.
3. Charge to 100% with the correct LiFePO4 settings. Victron recommends at least 2 hours in absorption each month so the cells can balance; the first spring charge is a good time to give it that.
4. Let the monitor resynchronize at full charge before trusting its percentage.
5. Test the bilge pump and alarms before launch.

Our Layup Checklist

1. Target 60% state of charge, unless your battery manual says otherwise. Mastervolt does.
2. Bring the bank to that level using the boat's own loads.
3. Chargers off, inverter off, loads off, network power off, main disconnect open, battery switched off or locked off.
4. Confirm zero current on the monitor.
5. Store it cool, not hot. No charging below 41°F unless the battery is heated and on a charger.
6. Check it on your manufacturer's schedule. Full charge in spring.

Planning a lithium upgrade over the winter instead? Start with our boat power usage audit template, then read How to Size a Boat Battery Bank and Going Lithium Without Going Wrong.

Want Us to Handle It?

Sea & Land Yacht Works winterizes and recommissions lithium systems from our shop in South Kingstown, Rhode Island, and at marinas across Rhode Island, Connecticut and Massachusetts. We will set the storage charge to your manufacturer's spec, find the parasitic loads and isolate the bank properly. Call 401-753-7479 or request a consultation. Browse the lithium batteries, MG Master LV battery management and meters and monitoring we carry.

Sources

• Epoch Batteries, How to Store LiFePO4 Lithium Batteries for Winter, updated October 2026
• Victron Energy, Lithium Battery Smart manual, Lithium NG battery manual, Lithium SuperPack NG manual, Lithium Smart and NG datasheets, and lithium battery safety data sheets (Section 7, Handling and Storage)
• MG Energy Systems, MG Master LV manual, version 2.0, and MG LFP battery technical specifications
• Mastervolt, MLI Ultra Lithium-Ion Battery 12/3000, 12/6000, 24/6000 user and installation manual (Sections 9, 11 and 17)
• Keil et al., Calendar Aging of Lithium-Ion Batteries, Journal of The Electrochemical Society, 2016

Mike Garretson is an ABYC Master Technician and the owner of Sea & Land Yacht Works. He writes about marine electrical systems for Soundings magazine.