A flat battery at the start of a trip (or after winter storage) is a quick way to spoil your plans. With a little planning, you can size, choose, and care for your leisure battery so your lights, pumps, and fridge keep running without stress. This guide covers battery types, sizing, runtime, replacement signs, and practical safety tips for installation and storage.
Battery types explained
You will see four main leisure battery types in the UK market. Each suits a different use pattern and budget.
- Flooded lead acid: Traditional and low cost. Needs ventilation and occasional maintenance. Best for light cycling on hook-up.
- AGM: Sealed, spill-resistant, and vibration-tolerant. Good charge acceptance and reliable for weekenders, winter storage, and moderate off-grid use.
- Gel: Stable at slow discharge and in low temperatures. Charges more slowly and costs more than AGM. Suits sensitive electronics and infrequent deep cycles.
- Lithium iron phosphate (LiFePO4): Light, fast charging, deep usable capacity, long cycle life. Higher upfront cost and needs a suitable charger plus a battery management system. Ideal for frequent off-grid touring and heavier 12V loads.
If you spend most nights on electric hook-up, AGM usually offers the best balance of cost and reliability. If you tour off-grid and want low weight and long life, LiFePO4 is the premium choice.
What size leisure battery do you need?
Sizing starts with your daily consumption. List each 12V load, note amps, and how many hours you use it.
- LED lights: 1 to 3A total for 3 hours, around 3 to 9Ah
- Water pump: roughly 4 to 6A for 15 minutes, around 1 to 1.5Ah
- Control panel, alarms, standby: 0.5A for 24 hours, around 12Ah
- Vent fan: 1 to 2A for 2 hours, around 2 to 4Ah
- Compressor 12V fridge: 3 to 5A average duty cycle for 24 hours, around 36 to 60Ah depending on temperature and insulation
How to calculate: add up the amp-hours, add 20% headroom, then adjust for usable capacity.
- Lead acid (flooded, AGM, gel): aim to avoid going below about 50% for good lifespan.
- Lithium (LiFePO4): often offers 80% to 90% usable capacity.
Example: a weekend setup with LED lighting, pump, controls, fan, and a compressor fridge might use 60 to 80Ah per day. For AGM you would target 120 to 160Ah bank capacity. For lithium, a single 100Ah pack can often handle that daily use with margin.
Space, weight, and venting also influence the right choice. Measure your battery tray, check hold-down options, and verify cable routes before you buy.
What can you run from a 12V leisure battery?
Typical 12V loads include lighting, fans, control systems, phone charging, water pumps, diesel or gas heaters, TVs, routers, and efficient fridges.
Important: resistive heating and standard kettles are not realistic on battery power. If you plan to use mains appliances, calculate their watt draw and consider an inverter. Pair any inverter with correct fusing, cable size, and ventilation.
How long will a motorhome battery last on a trip?
Runtime depends on usable capacity and load. As a simple rule of thumb:
- 100Ah AGM: about 50Ah usable. At a steady 5A load, roughly 10 hours to reach 50% state of charge.
- 100Ah LiFePO4: about 80 to 90Ah usable. At 5A load, roughly 16 to 18 hours.
Real world use is a mix of intermittent loads and charging from driving, solar, or hook-up. A 100W solar panel can add around 20 to 35Ah on a bright day. Add more solar for longer stays in one place.
Signs your caravan battery needs replacing
Replace your battery if you notice any of the following:
- Rapid voltage sag under small loads
- Resting voltage dropping below 12.4V after a full charge
- Swelling, leaks, or a cracked case
- Strong sulphur smell or excessive heat when charging
- Capacity loss (lights dim, pump stutters after short use)
- Fails a simple capacity test (fully charge, run a known 5A load, time to 12.0V under load, then compare to rated capacity and chemistry guidance)
Most lead acid leisure batteries last around 3 to 6 years with correct charging. Lithium units can exceed 10 years or 2,000+ cycles if managed well.
Best leisure battery picks (by touring style)
- Hook-up most nights, light off-grid: AGM 90 to 110Ah. Sealed, reliable, and good value.
- Balanced touring with some wild camping: AGM 120 to 140Ah, or two 90Ah batteries in parallel for redundancy. Check your charger can deliver at least 10% of total Ah.
- Frequent off-grid, power-hungry loads, winter travel: LiFePO4 100 to 200Ah with low temperature charge protection, internal BMS, and a charger or DC-DC unit that supports lithium profiles.
If weight is critical in a smaller van, lithium can save around 10 to 20kg per 100Ah compared with AGM.
Installation and safety basics
- Cables: use the correct cable cross-section for expected current. Inverters can draw 100A or more, so oversize cables and keep runs short.
- Fusing: fit a main fuse within 200mm of the positive terminal. Size the fuse to protect the smallest cable in the circuit.
- Ventilation: flooded batteries must be vented outside. Sealed lead acid still benefits from airflow. Keep lithium in a dry, stable space away from heat sources.
- Charging: match charger profile to chemistry. Consider a DC-DC charger when charging from the alternator, especially with smart alternators and lithium banks.
- Isolation: fit a master cut-off switch and label it.
- Monitoring: a voltmeter helps, but a shunt-based monitor gives far more accurate state of charge readings.
Battery care tips (storage and season prep)
- Keep it charged: store lead acid fully charged. For long-term lithium storage, aim for 40% to 60% and top up every 2 to 3 months.
- Protect from deep discharge: do not run lead acid below 50% regularly. Set low voltage cut-offs on inverters.
- Maintain connections: clean terminals, check torque, inspect for corrosion or heat signs.
- Plan winter storage: isolate the battery and keep it above freezing. Remove parasitic draws unless needed for security.
- Test annually: do a capacity check before peak season so you can replace a weak unit before a long tour.
Quick runtime examples
These rough figures assume good batteries at room temperature.
- LED interior lights (12W total, about 1A): 50Ah usable provides roughly 40 to 45 hours of lighting.
- TV and router (4A combined): around 12 hours on 50Ah usable.
- Compressor fridge (around 40Ah per day): a 100Ah AGM bank (around 50Ah usable) supports roughly one day plus margin. Add solar or driving time to extend.
Useful accessories to round out your setup
- Battery monitor and shunt for accurate state of charge
- DC-DC charger if your vehicle has a smart alternator
- Solar controller matched to panel size and battery chemistry
- Spare fuses, lugs, and quality crimping
- Efficient 12V lighting to cut draw at night
Helpful links
- Planning a full setup or upgrade? Read: Campervan electrics: what you need and how to get powered up
- Tour off-grid and want to keep batteries topped up? See: 100W caravan solar panel kit (inc fittings and wiring)
- Reducing power draw helps battery life. Read: Lighting up your awning: easy tips and must-have accessories
Summary
Choose battery chemistry to match your touring style. Size your battery bank from daily amp-hour use, then add headroom and account for usable capacity by chemistry. Watch for signs of ageing so you can replace a weak unit before it lets you down. Fit correct fusing and cable sizes, and use a charger profile that matches your battery type. For longer stays away from hook-up, add solar and consider a lithium upgrade. With a well-planned system and a few careful habits, your caravan or motorhome will power lights, pumps, controls, and a reliable fridge through every season.