How to Winterise a Leisure Battery in a Campervan

If your campervan is off the road over winter, the way you store the leisure battery significantly affects how long it lasts. The wrong approach — leaving a discharged AGM in a cold garage — can write off a battery over one winter.

AGM and lead-acid batteries in winter storage

Lead-acid chemistry (AGM, gel, flooded) is sensitive to both cold temperatures and discharge state.

Cold temperature effect: A fully charged AGM can tolerate temperatures well below freezing without damage. A discharged AGM electrolyte has a higher freezing point and can freeze at -15°C, cracking the plates. Keep AGM batteries at least partially charged through winter.

Self-discharge: AGM batteries self-discharge at approximately 3–5% per month. Over a 5-month winter, a battery will lose 15–25% of charge. A battery that starts at 50% charge in October may be dangerously discharged by March.

Sulphation: Lead-acid batteries left in a partially discharged state develop lead sulphate crystals on the plates (sulphation), which reduce capacity permanently. The longer the battery sits discharged, the more damage occurs.

AGM winter storage procedure

1. Bring the battery to full charge (14.4–14.7V absorption, current falls to under 2A)
2. Store in a cool (not freezing), dry location — ideally between 5°C and 15°C
3. Connect a maintenance charger (CTEK MXS 5.0, Optimate) set to long-term maintenance mode — this delivers a tiny float charge to offset self-discharge
4. Check voltage every 4–6 weeks; recharge if it falls below 12.4V

LiFePO4 batteries in winter storage

LiFePO4 handles winter storage much better than AGM.

Self-discharge: LiFePO4 loses only 1–2% per month. A fully charged battery stored in October will still be at ~90% in March without any maintenance charging.

Cold temperature: LiFePO4 cells should not be charged below 0°C (the BMS disconnects charging to prevent lithium plating). Discharge at low temperatures is possible but capacity is reduced. Storage at cold temperatures does not damage LiFePO4 cells.

Optimal storage charge: 50–60% SoC is ideal for long-term storage. At full charge, LiFePO4 cells experience slightly more stress over time. Storing at 50% (approximately 13.2V resting) minimises degradation.

LiFePO4 winter storage procedure

1. Discharge to approximately 50% (resting voltage ~13.2V)
2. Store anywhere above -20°C — a cold garage is fine for LiFePO4
3. No maintenance charger needed
4. Reconnect and check in spring before use

Leaving solar connected in winter

If your campervan is parked but accessible to sunlight, leaving the solar array connected through winter is often the easiest approach. Even in low winter sun, a 100W panel can deliver 10–20Ah per day, more than enough to offset self-discharge and keep batteries topped up. The MPPT controller manages the charging correctly.

Ensure your charge controller is set for the correct chemistry and winter float voltage.

What to check in spring

AGM batteries:

• Take a resting voltage reading 24 hours after charging — should read 12.7V or higher
• Load test with a battery load tester — capacity degradation shows as voltage sag under load
• Check for any physical swelling of the case (a sign of overcharge or freezing damage)

LiFePO4 batteries:

• Check resting voltage — should be close to storage level (if stored at 50%, expect ~13.2V)
• Do a full charge-discharge cycle to re-calibrate the battery monitor
• Check BMS via app (Victron, JK, or manufacturer app) for any fault logs

FAQ

Can I leave an AGM battery in the van over winter without a maintenance charger?

Only if the van is fully charged and parked somewhere above freezing, and you plan to check it every 4–6 weeks. A maintenance charger is much safer and costs under £30.

Does a LiFePO4 battery need a maintenance charger in winter?

No — the low self-discharge rate means a LiFePO4 can sit for 6 months without supervision and still have plenty of charge. Store at 50% SoC and leave it.

Will cold weather permanently damage my LiFePO4?

Cold storage does not damage LiFePO4 cells. Cold charging does — the BMS prevents this by disconnecting when cell temperature drops below 0°C. If you need to charge a cold LiFePO4, warm the battery first or use a self-heating battery (Victron SmartLithium, Battle Born heated).