What Size Leisure Battery Do I Need? (Calculator + Guide)

Choosing the right size leisure battery is one of the most important decisions in any campervan build. Too small and you run out of power mid-trip. Too large and you waste money, weight, and space on capacity you never use. The sweet spot depends on what you run, how you charge, and how you use your van.

This guide walks through exactly how to calculate the right battery size for your setup. It sits within our comprehensive campervan battery guide, which covers chemistry types, wiring, and maintenance in detail. If you want the quick answer, our calculator does all the maths automatically — enter your appliances and it tells you exactly what capacity you need.

The Formula: How Battery Sizing Works

Battery sizing follows a straightforward formula:

Daily consumption (Wh) x Days of autonomy / Usable depth of discharge = Required battery capacity (Wh)

Then convert to amp-hours: Wh / System voltage (12V) = Ah

Let us break down each part.

1. Daily Consumption

This is how much energy you use per day, measured in watt-hours (Wh). You calculate it by multiplying each appliance's power draw (watts) by the number of hours you use it daily.

For a detailed walkthrough of this process, see our power audit guide.

Here are three realistic UK campervan scenarios:

Basic Weekend Van

Comfortable Touring Van

Full-Time Remote Worker

2. Days of Autonomy

This is how many days you want your battery to last without any charging input — no solar, no driving, no hook-up. This buffer accounts for worst-case scenarios: consecutive overcast days, being parked without driving, or equipment issues.

Recommended autonomy by use case:

3. Usable Depth of Discharge

You cannot use 100% of a battery's rated capacity. How much you can actually use depends on the battery chemistry:

• LiFePO4 (Lithium): 80-90% usable (we recommend calculating at 80%)
• AGM: 50% usable (discharging deeper than 50% significantly shortens lifespan)
• Standard Lead-Acid: 50% usable
• Gel: 50-60% usable

This is a crucial difference. A 200Ah LiFePO4 battery gives you 1,920 Wh of usable energy (200 x 12 x 0.8). A 200Ah AGM battery gives you only 1,200 Wh of usable energy (200 x 12 x 0.5). For a full comparison of these chemistries, see our LiFePO4 vs AGM guide.

Worked Examples

Example 1: Weekend Warrior

Profile: Uses the van on weekends and holidays. Drives to a new spot most days. Basic needs — fridge, lights, phone charging.

• Daily consumption: 648 Wh
• Autonomy needed: 1.5 days
• Battery chemistry: LiFePO4
• Required capacity: 648 x 1.5 / 0.8 = 1,215 Wh = 101 Ah

Recommendation: 100Ah LiFePO4 — this is the minimum viable leisure battery for a campervan with a fridge. It covers a full day plus a comfortable buffer, and regular driving with a DC-DC charger keeps it topped up.

Example 2: Comfortable Tourer

Profile: Takes 2-4 week trips multiple times per year. Mix of driving days and stationary days. Runs a laptop, heater, and all the basics.

• Daily consumption: 1,104 Wh
• Autonomy needed: 2 days
• Battery chemistry: LiFePO4
• Required capacity: 1,104 x 2 / 0.8 = 2,760 Wh = 230 Ah

Recommendation: 200-300Ah LiFePO4 — 200Ah is workable if you have good solar and drive regularly. 300Ah gives genuine peace of mind for extended stationary stays.

Example 3: Full-Time Remote Worker

Profile: Lives in the van year-round. Works remotely with laptop and Starlink. Needs reliable power through UK winter.

• Daily consumption: 1,964 Wh
• Autonomy needed: 2.5 days
• Battery chemistry: LiFePO4
• Required capacity: 1,964 x 2.5 / 0.8 = 6,138 Wh = 511 Ah

Recommendation: 400-600Ah LiFePO4 — this is a serious system, but it reflects genuine full-time needs. Many full-time van lifers in the UK run 400Ah and manage through careful consumption habits and multi-source charging.

Common Battery Sizes and Who They Suit

100Ah LiFePO4 (1,200 Wh usable)

Best for: Weekend vans with basic needs. Fridge, lights, phone charging, and perhaps a small fan.

Limitations: No room for error. One day without charging and heavy usage will drain it. Not suitable if you run a laptop or diesel heater frequently.

Typical cost: £250-£500

200Ah LiFePO4 (2,400 Wh usable)

Best for: The most popular choice for UK campervan builds. Covers weekend and holiday use with comfortable margins, and can stretch to part-time use for moderate consumers.

Limitations: Tight for full-time living, especially in winter or with remote work equipment.

Typical cost: £500-£900

300Ah LiFePO4 (3,600 Wh usable)

Best for: Extended touring and moderate full-time use. Provides 2+ days of autonomy for most setups and charges back comfortably with 400W of solar in summer.

Limitations: Weighs approximately 35-40kg. Takes up more space. Higher cost.

Typical cost: £900-£1,500

400Ah+ LiFePO4 (4,800+ Wh usable)

Best for: Full-time living with high consumption — remote workers, Starlink users, winter van lifers. Provides the buffer needed for UK winter conditions.

Limitations: Significant weight (50-70kg), space requirements, and cost. Requires robust wiring and fusing.

Typical cost: £1,400-£2,500

For a detailed comparison of the two most popular sizes, see our 100Ah vs 200Ah leisure battery guide.

AGM vs LiFePO4: The Size Implications

Battery chemistry dramatically affects the physical size you need. Because AGM batteries can only be discharged to 50%, you need roughly 60% more rated capacity to achieve the same usable energy as LiFePO4.

To achieve 2,400 Wh usable:

The AGM option is cheaper but weighs roughly three times as much and takes up roughly twice the space. For most van builds where weight and space matter, LiFePO4 is the sensible choice despite the higher upfront cost.

The long-term cost picture favours lithium even more: LiFePO4 batteries last 3,000-6,000 cycles versus 400-800 for AGM. Over a 10-year period, you would likely replace AGM batteries 3-4 times while the lithium battery continues working.

Factors That Change Your Battery Size

Charging Sources

Your available charging sources directly affect how much battery capacity you need. More reliable charging means you can get away with a smaller battery:

• Solar + DC-DC + Shore Power: Full redundancy — battery mainly needs to cover overnight consumption. You can size more conservatively.
• Solar + DC-DC: The standard off-grid setup. Size for 1.5-2 days autonomy.
• DC-DC only: Viable if you drive daily. Size for 1-1.5 days autonomy.
• No charging while parked: You need the full autonomy calculation with no shortcuts.

Season of Use

If you only use your van from April to September, you can size your battery for summer conditions — shorter nights, less heater use, and stronger solar generation. This can reduce your required capacity by 20-30% compared with a year-round system.

If you use the van through UK winter, size for winter — longer heater runs, longer nights, and minimal solar assistance.

Location

Where you travel matters. UK van lifers who head south to Spain or Portugal in winter have far less challenging electrical conditions than those who stay in Scotland. A 200Ah bank that is marginal for a Scottish winter might be perfectly comfortable on the Algarve.

Inverter Losses

If you run 230V appliances through an inverter, add approximately 15% to those appliances' consumption to account for conversion losses. Also factor in the inverter's standby draw — typically 10-20W — for every hour it is switched on.

Quick Sizing Table

For those who want a fast answer:

Common Mistakes in Battery Sizing

1. Using Manufacturer's Ah Rating Without Considering DoD

A 200Ah AGM battery does not give you 200Ah. You get 100Ah usable. Always calculate on usable capacity.

2. Ignoring Seasonal Variation

If you plan your system for a sunny July weekend but then use the van in November, you will be disappointed. Size for your worst-case month.

3. Forgetting About Peukert's Effect (AGM Only)

AGM and lead-acid batteries deliver less capacity at higher discharge rates. If you draw 20A continuously from a 100Ah AGM battery, you may get less than the rated 100Ah. This effect does not apply to lithium batteries, which deliver their full rated capacity regardless of discharge rate.

4. Not Accounting for Battery Degradation

All batteries lose capacity over time. A 200Ah lithium battery might deliver 180Ah after 2,000 cycles. Build in a small margin — if the formula says you need 190Ah, go for 200Ah, not 150Ah.

5. Confusing Ah with Wh

A 100Ah battery at 12V stores 1,200 Wh. A 100Ah battery at 24V stores 2,400 Wh. Always check whether discussions and calculations are in Ah or Wh, and at what voltage.

FAQ

What size leisure battery do I need for a fridge?

A compressor fridge typically uses 500-600 Wh per day. For fridge-only use with daily driving (DC-DC charging), a 100Ah LiFePO4 battery is sufficient. If you also run lights, phone charging, and other basics, step up to 200Ah.

Is 100Ah enough for a campervan?

For weekend use with basic needs (fridge, lights, phone charging) and daily driving, yes. For anything beyond that — laptop use, diesel heater, extended parking, or winter use — 200Ah is a more comfortable choice.

Is 200Ah enough for full-time van life?

It is tight but workable for disciplined users with good solar and regular driving. Most full-time van lifers in the UK find 300Ah more comfortable, and remote workers should consider 400Ah.

How many amp-hours do I need per day in a campervan?

A basic van uses approximately 50-60Ah per day at 12V. A comfortable touring setup uses 80-100Ah per day. A full-time setup with work equipment uses 150-200Ah per day. These figures assume a 12V system.

Should I get one large battery or two smaller ones?

Two smaller batteries offer redundancy — if one fails, you still have power. However, a single larger battery is simpler to wire, lighter per Ah, and often cheaper per Ah. For critical applications (full-time living), two batteries are worth considering. For weekend use, a single battery keeps things simple.