How to Size a Lithium Battery Bank for a Campervan

Getting the right battery bank size is critical for a campervan electrical system. Too small, and you'll run out of power before morning. Too large, and you've wasted money and added unnecessary weight. This guide walks through a practical sizing process using Victron Lithium Smart batteries, with real-world examples for common campervan builds in the UK.

Step 1: Calculate Your Daily Energy Usage

Before you can size a battery, you need to know how much energy you use per day. List every electrical device in your campervan, its wattage, and how many hours per day you'll use it.

Subtotal: approximately 860Wh/day (this is a fairly typical full-time campervan build)

If you use an inverter for AC appliances, add those too — but factor in ~90% inverter efficiency. For a more detailed energy calculation including solar sizing, see our solar sizing guide.

Step 2: Determine Days of Autonomy

Your battery needs to cover periods when charging is limited — cloudy days, long evenings in Scotland, or days when you're parked under trees with no solar. The standard recommendation is:

• 1.5 days of autonomy: Minimum for UK campervans with solar — covers one cloudy day with a comfortable margin
• 2 days of autonomy: Recommended for winter use or northern Scotland trips where solar yield can be very low for extended periods
• 1 day of autonomy: Acceptable if you have reliable alternator charging (driving every day) or a shore power hookup available

For our 860Wh/day example:

• 1.5 days = 1,290Wh of usable battery capacity needed
• 2 days = 1,720Wh of usable battery capacity needed

Step 3: Convert Wh to Ah

Battery capacity is rated in amp-hours (Ah) at a specific voltage. The Victron Lithium Smart range operates at 12.8V nominal. To convert:

Ah = Wh / Voltage

• 1,290Wh / 12.8V = 101Ah
• 1,720Wh / 12.8V = 134Ah

Step 4: Account for Usable Capacity

LiFePO4 batteries shouldn't be regularly discharged below 20% SOC for optimal lifespan. This means only 80% of the rated capacity is usable on a daily basis.

Adjust the required capacity:

• 101Ah / 0.80 = 126Ah rated capacity (for 1.5 days autonomy)
• 134Ah / 0.80 = 168Ah rated capacity (for 2 days autonomy)

Step 5: Factor in Inverter Surge Current

Your battery bank must also handle the maximum discharge current your system demands. If you have a MultiPlus 12/2000, it can draw up to approximately 180A from the battery at full load, plus brief surge currents up to 250A when starting motors or compressors.

Victron Lithium Smart batteries can deliver:

A single 100Ah Victron Lithium Smart can handle a 2000W inverter comfortably. For a 3000W inverter (250A continuous), you'd want at least 150Ah or two 100Ah batteries in parallel.

Step 6: Choose Your Battery Configuration

Based on the calculations above, here are the most common configurations for UK campervan builds:

Light Use (400–600Wh/day)

Typical for weekend campervans with LED lights, a small fridge, phone charging, and a water pump. No inverter or only a small one for occasional laptop charging.

• Recommended: 1x Victron Lithium Smart 100Ah 12.8V
• Usable capacity: 80Ah (1,024Wh)
• Autonomy: 1.7–2.5 days
• Weight: 12kg
• Approximate cost: £750–£950

Medium Use (600–1000Wh/day)

Typical for full-time campervans with a full-size fridge, LED lighting, diesel heater, laptop charging, and occasional inverter use for small appliances.

• Recommended: 1x Victron Lithium Smart 200Ah 12.8V (or 2x 100Ah in parallel)
• Usable capacity: 160Ah (2,048Wh)
• Autonomy: 2–3 days
• Weight: 22kg (single 200Ah) or 24kg (2x 100Ah)
• Approximate cost: £1,400–£1,700

Heavy Use (1000–1500Wh/day)

Full-time builds with regular inverter use — coffee machine, hair dryer, power tools, electric blanket, multiple device charging, and a large fridge-freezer.

• Recommended: 2x Victron Lithium Smart 200Ah 12.8V in parallel (400Ah total) or 1x 200Ah + 1x 100Ah (300Ah total)
• Usable capacity: 240–320Ah (3,072–4,096Wh)
• Autonomy: 2–4 days
• Weight: 34–44kg
• Approximate cost: £2,100–£3,400

Parallel Batteries: More Capacity

You can connect multiple Victron Lithium Smart batteries in parallel (positive to positive, negative to negative) to increase total capacity while staying at 12.8V. Victron allows up to 5 batteries in parallel with the Lithium Smart range.

When connecting in parallel:

• Use identical batteries (same model, same age ideally)
• Use equal-length cables from each battery to the busbar
• Each battery's internal BMS operates independently — if one BMS trips, the others continue operating
• Total capacity and discharge current both increase proportionally

Physical Size and Weight Constraints

Before finalising your battery choice, check the physical dimensions against your available space:

The 100Ah battery fits under most campervan seats and in standard battery boxes. The 200Ah battery is significantly larger — measure your intended location carefully before purchasing. Two 100Ah batteries side by side may fit a space where a single 200Ah battery won't, or vice versa.

Weight matters — a 200Ah lithium battery at 22kg is far lighter than equivalent AGM capacity (~120kg for 400Ah at 50% usable depth).

Common Sizing Mistakes

• Oversizing: A 400Ah bank for a weekend campervan that uses 300Wh/day is wasted money and weight. You'll never discharge below 90% SOC.
• Undersizing: A 100Ah bank for a full-time van with a 2000W inverter, electric kettle, and hair dryer will be empty by lunchtime on a cloudy day.
• Ignoring winter: If you plan to use the van year-round in the UK, size for winter conditions. Solar yield in December is roughly 15–20% of summer yield. Your battery bank needs to carry you through dark, short days.
• Forgetting inverter losses: Any AC power drawn through an inverter loses approximately 10% to conversion inefficiency. A 1000W load actually draws about 1100W from the battery.
• Not accounting for vampire loads: The fridge, diesel heater controller standby, and Cerbo GX all draw power 24/7 — these add up to 200–400Wh/day

Summary

To size a lithium battery bank for your campervan: calculate your daily energy usage in Wh, multiply by your desired days of autonomy (1.5–2), divide by 12.8V to get Ah, then divide by 0.80 to account for usable capacity. For most UK campervans, this lands between 100Ah and 300Ah of Victron Lithium Smart capacity. A single 100Ah battery suits light weekend use; 200Ah is the full-timer's standard; and 300Ah+ is for heavy users or winter travellers who need maximum independence. Always verify that your battery bank can handle your inverter's peak current draw, and double-check the physical dimensions against your available installation space.