Camper and Boat Battery Winter Storage: Disconnect, Maintain or Remove?

Most leisure batteries that die over winter are not killed by the cold. They are drained flat by small loads nobody switched off, and a flat lead-acid battery then sulphates or freezes, while a flat LiFePO4 battery can drop below the voltage its cells survive. November is when motorhomes, caravans and boats go into storage: the German motoring clubs ACV and ADAC Hessen-Thüringen published lay-up checklists on 13 and 28 October 2026, and in the latest week, German searches for "Erhaltungsladegerät" (battery maintainer) and "Batterietrennschalter" (battery disconnect switch) rose by about 22 to 24 % on the week before (Google Trends).

This is a researched guide, not a hands-on test. The figures come from the manuals and data sheets of the battery, charger and relay makers named below.

The short version

• Bring the battery to the storage charge its manual asks for. Lead-acid and AGM: fully charged. LiFePO4: it depends on the maker. Renogy asks for 30 to 50 % before storage, Victron rates its Lithium Smart batteries for one year of storage at 25 °C when fully charged.
• Disconnect it. A main switch stops most standby loads, but not the ones wired ahead of it. Over a 150-day lay-up, 30 mA of standby current adds up to 108 Ah, more than a 100 Ah battery holds.
• Check it, or maintain it. Lead-acid every 6 to 8 weeks or on a maintainer with a float or storage stage; LiFePO4 every 3 to 6 months (Renogy). Never charge LiFePO4 below 0 °C.
• Do not forget the starter battery. It has its own standby loads and usually no charger during storage.

Why a battery goes flat in storage

Two things drain a battery that nobody uses.

Self-discharge. It is small. Victron gives less than 2 % per month at 20 °C for its AGM and gel batteries, doubling with every 10 °C warmer. A cold winter garage slows it down further.

Standby loads. These are the real problem. Every device that stays connected draws a few milliamps around the clock, and over months that becomes amp-hours:

• A Victron BMV-712 battery monitor draws under 1 mA with the backlight off. Victron's own manual still asks you to disconnect the supply when a lithium system is left unattended for a long time.
• A Blue Sea SI-ACR automatic charging relay draws 15 mA while open and 175 mA while it holds the batteries together.
• Gas alarms, trackers, radio memories, a solar charge controller at night and the chassis electronics of the base vehicle all add their share. Their draw is rarely on the label; a clamp meter or a shunt monitor shows the total.

The arithmetic is simple: milliamps × 24 h × days ÷ 1000 = Ah. One milliamp costs 3.6 Ah over a 150-day lay-up, 30 mA cost 108 Ah. Victron puts it the same way in the BMV manual: 1 mA left on a discharged 100 Ah battery for 40 days takes another 0.96 Ah, enough to damage it.

You can run the same check for your own build: enter the battery capacity and the standby draw as a load in the battery runtime calculator. At 12.8 V, 30 mA is about 0.4 W.

Storing a LiFePO4 battery

LiFePO4 copes with cold storage far better than with cold charging. Renogy's Core Series manual allows storage from -25 to 65 °C and Victron lists -45 to 70 °C for its Lithium Smart batteries, but charging is another matter: Victron allows it only from 5 °C, and most LiFePO4 batteries must not be charged below 0 °C (see our guide to LiFePO4 cold charging).

What the makers ask for differs:

	Renogy Core Series manual	Victron Lithium Smart manual
Charge level before storage	30 to 50 %	Storage time rated "when fully charged"
Storage temperature	-25 to 65 °C	-45 to 70 °C
During storage	Disconnect from the system, charge at least every 3 to 6 months	Up to 1 year at 25 °C
After storage	Charge fully	-

Follow the manual of your own battery, because the warranty usually depends on it; Renogy states that ignoring its storage steps voids the warranty. In practice that means: set the charge level, turn the battery off with its own switch or the main switch, and check the voltage or the app every few months.

A maintainer for LiFePO4? Usually not needed. If you do want the battery on charge, use a charger with a lithium profile and make sure the battery stays above 0 °C. Victron says a storage stage is not needed for lithium and should be set to the float voltage of 13.5 V if the charger has one. The CTEK Lithium XS is built for 12 V LiFePO4: it charges 5 to 60 Ah and maintains up to 120 Ah, and it resets a battery whose low-voltage protection has tripped. For a 200 Ah house bank, it is a maintainer, not a charger.

Storing a lead-acid, AGM or gel battery

Lead-acid has the opposite problem: it must not sit partly discharged. A discharged lead-acid battery sulphates, and the more it is discharged, the weaker its electrolyte gets and the sooner it can freeze. So the rule is: fully charged in, and kept full.

There are two ways to do that:

1. Charge, disconnect, recharge. Charge fully, open the main switch and recharge every 6 to 8 weeks, as the motorhome magazine promobil recommends (16 October 2026). With Victron's self-discharge figure, a cold, disconnected AGM battery loses only a few percent in that time; the standby loads are what you are guarding against.
2. Leave it on a maintainer. A charger with a float or storage stage keeps the battery full for months, provided there is mains power where the vehicle stands.

Suitable maintainers we have added to the catalogue:

Charger	Battery types	Current	Battery size (manufacturer)	Worth knowing
CTEK MXS 5.0	12 V lead-acid (WET, MF, Ca/Ca, AGM, EFB, GEL)	5 A	1.2 to 110 Ah	Float/pulse maintenance, Recond mode at 15.8 V
CTEK MXS 10	12 V lead-acid (WET, MF, Ca/Ca, AGM, GEL)	10 A	20 to 200 Ah, maintains up to 300 Ah	13.6 V supply mode
NOCO GENIUS10	6 and 12 V lead-acid, 12 V lithium with BMS	10 A	up to 230 Ah, maintains all sizes	100 to 240 V input, back drain under 0.5 mA, IP65
CTEK Lithium XS	12 V LiFePO4	5 A	5 to 60 Ah, maintains up to 120 Ah	Resets a tripped low-voltage protection
Victron Blue Smart IP65 12/10	Lead-acid and Li-ion modes	10 A	-	Storage stage at 13.2 V (lead-acid), 1 h absorption every 7 days

The CTEK links go to the 230 V versions; CTEK's North American MXS 5.0 and Lithium US are 4.3 A models for 110 to 120 V, so check the data sheet of the version sold in your country. Prices for all of these change often, so check the current price at the retailer.

Two practical points:

• Connect the maintainer at the battery terminals, not somewhere behind the main switch. Otherwise opening the switch for storage also disconnects the charger. A charger that is permanently installed needs its own fuse close to the battery positive.
• Turn Recond and desulphation modes off for AGM and gel unless the battery maker allows them. The CTEK MXS 5.0 and MXS 10 reach 15.8 V in that step. Flooded batteries give off gas while charging; charge them in a ventilated space.

The starter battery

The base vehicle's battery is drained by its own electronics, and a shore-power charger in the living area usually charges only the house battery. promobil suggests disconnecting the negative terminal of the starter battery for long lay-ups. Alternatives:

• a separate maintainer on the starter battery, for example the CTEK MXS 5.0 for lead-acid;
• an automatic charging relay, which joins the two batteries whenever one of them is being charged. The Blue Sea Systems SI-ACR is dual-sensing: a charger or solar on either battery closes it once the voltage reaches 13.6 V for 30 seconds or 13.0 V for two minutes, and it opens again at 12.75 V for 30 seconds or 12.35 V for 10 seconds.

The relay has a catch with lithium. Victron's manual expects a charged LiFePO4 battery to rest at 13.2 V or higher. That is above the SI-ACR's 13.0 V close threshold and its 12.75 V open threshold, so a full lithium bank can hold the relay closed. The relay then draws its own 175 mA and lets the house bank feed the starter battery. The relay alone costs 4.2 Ah a day, almost 30 Ah a week, until the bank's voltage falls below the open threshold. For a LiFePO4 house bank, a DC-DC charger such as the Victron Orion XS is the better link to the alternator. For storage, open the main switch and use a separate maintainer on the starter battery. Our DC-DC charger comparison covers the options for driving.

What the main switch does not disconnect

A main switch in the battery positive is the quickest way to stop standby loads. Readers of our guides clicked through to shop for a Blue Sea battery switch 17 times in the last 30 days. We have not added the switches to the catalogue yet, so the link goes to an Amazon search for the Blue Sea Systems m-Series battery switch. Before you rely on a switch, check what is wired ahead of it:

• The battery monitor. Its supply wire usually goes straight to the battery positive through its own fuse. Victron's BMV manual tells you to interrupt that supply as well for long lay-ups with lithium batteries; pull the fuse. Our battery monitor installation guide shows where that wire sits.
• Charging relays and DC-DC chargers connected directly at the battery.
• Alarm systems and trackers, which installers often wire to the battery on purpose.
• The starter battery circuit, which a house-battery switch does not touch.

If you are not sure, measure: with everything off and the switch open, a clamp meter on the battery cable should show close to 0 A.

Remove the battery or leave it in?

You do not have to remove it. promobil's advice matches the manufacturers': a disconnected, correctly charged battery can stay in the vehicle. Removal makes sense for a lead-acid battery in a vehicle that stands outside in hard frost without mains power, because a frost-free cellar and a maintainer are the safest combination for it. A LiFePO4 battery can stay in a cold vehicle as long as nothing tries to charge it below 0 °C, and that includes the solar panel on the roof. If the solar charge controller has no low-temperature cut-off and the battery has no protection or heater of its own (see our self-heating LiFePO4 comparison), switch the solar input off for the winter.

Plan it in the diagram

Put the batteries, main switch, relay or DC-DC charger, maintainer and battery monitor into the free VoltPlan diagram editor. It shows which devices sit ahead of the main switch and sizes the cables and fuses for every charge path, so the winter set-up is clear before you lock up the vehicle.

FAQ

Should I remove my camper battery for the winter?

It is not necessary. Charge it to the level its manual asks for, disconnect it with the main switch or by removing the negative cable, and check it every few weeks. Removing a lead-acid battery into a frost-free room with a maintainer is the safest option if the vehicle stands outside in frost without mains power.

Can I leave a battery maintainer connected all winter?

Yes, for lead-acid, AGM and gel batteries, as long as the charger has a float or storage stage such as the CTEK MXS series, the NOCO GENIUS10 or the Victron Blue Smart. For LiFePO4, use a charger with a lithium profile and only while the battery is above 0 °C. Victron says a storage stage is not needed for lithium.

What charge level should a LiFePO4 battery have for storage?

Whatever its manual says. Renogy asks for 30 to 50 % and a top-up charge every 3 to 6 months; Victron rates its Lithium Smart batteries for one year at 25 °C when fully charged. Never store LiFePO4 empty: standby loads and self-discharge can then pull the cells below their minimum voltage.

How much does a small standby load drain over winter?

Multiply milliamps by 24 hours and by the number of days, then divide by 1000 to get Ah. Over 150 days, 1 mA uses 3.6 Ah and 30 mA uses 108 Ah. The battery runtime calculator does this for any battery size.

Will an automatic charging relay keep my starter battery charged in storage?

Only while a charger or solar panel is charging one of the batteries. Blue Sea's SI-ACR closes at 13.6 V for 30 seconds or 13.0 V for two minutes and draws 175 mA while closed. A full LiFePO4 house bank rests at 13.2 V or higher, so the relay can stay closed and drain the house bank, so use a DC-DC charger with lithium and a separate maintainer for the starter battery.

Does the main switch stop all parasitic drains?

Only those behind it. Battery monitors, charging relays, DC-DC chargers and alarm systems are often wired directly to the battery. Pull their fuses as well and check with a clamp meter that close to 0 A flows.