Battery capacity is one of the most misunderstood aspects of campervan electrical systems.
Some travellers install massive battery banks they rarely use, while others discover too late that their batteries cannot support their daily energy needs.
The right battery capacity depends on how you travel, what equipment you use and how often you expect to recharge.
This guide explains how to calculate realistic battery requirements and avoid spending money on capacity you don’t need or, worse, discovering you don’t have enough.
For a complete overview of campervan power systems, see Campervan Electrical & Solar Systems.
Why Battery Capacity Matters
Your battery bank determines how long you can operate without external charging.
A properly sized battery system provides:
- Greater off-grid freedom
- Improved reliability
- Reduced generator or campsite dependence
- Better battery lifespan
- Lower long-term costs
The goal is not simply to install the largest battery possible but to match capacity to actual usage.
Understanding Battery Capacity
Battery capacity is typically measured in:
Amp Hours (Ah)
The most common rating used by battery manufacturers.
Watt Hours (Wh)
Often more useful for calculating real-world energy usage.
The conversion is simple:
Amp Hours × Voltage = Watt Hours
Example:
100Ah Lithium Battery
100 × 12.8V
= 1,280Wh
This figure represents the total energy stored within the battery.
Usable Capacity Matters More Than Total Capacity
Not all battery technologies allow full discharge.
AGM Battery
Typical usable capacity:
50%
Example:
100Ah AGM
≈ 50Ah usable
≈ 640Wh usable
Lithium Battery
Typical usable capacity:
80–100%
Example:
100Ah Lithium
≈ 100Ah usable
≈ 1,280Wh usable
This is one reason lithium batteries have become increasingly popular despite their higher upfront cost.
Step 1: Calculate Daily Energy Usage
Before sizing batteries, calculate how much electricity you consume each day.
Examples:
| Device | Daily Consumption |
| Fridge | 400Wh |
| Lighting | 50Wh |
| Water Pump | 20Wh |
| Laptop | 300Wh |
| Phone Charging | 50Wh |
| Heater Controls | 100Wh |
Total:
920Wh per day
Your battery system must support this demand.
For a detailed breakdown, see Solar Power Calculations for UK Vanlife.
Step 2: Decide How Long You Want to Stay Off-Grid
Battery capacity should reflect how many days you wish to operate without charging.
Examples:
One Day Off-Grid
920Wh required
Two Days Off-Grid
1,840Wh required
Three Days Off-Grid
2,760Wh required
This is often referred to as your energy reserve.
Step 3: Add a Safety Margin
Real-world conditions are rarely perfect.
Unexpected energy use may include:
- Poor weather
- Additional heating
- Device charging
- Extended stays
- Reduced solar production
A safety margin of 20–30% is usually sensible.
Example:
2,760Wh
Plus 25%
= 3,450Wh target capacity
This provides useful flexibility.
Typical Battery Requirements by Travel Style
Weekend Traveller
Energy usage:
300–800Wh per day
Recommended:
100Ah Lithium
Suitable for:
- Lighting
- Fridge
- Device charging
Touring Couple
Energy usage:
800–1,500Wh per day
Recommended:
150–200Ah Lithium
Provides comfortable off-grid capability.
Remote Worker
Energy usage:
1,500–2,500Wh per day
Recommended:
200–300Ah Lithium
Supports laptops, routers and extended device use.
Full-Time Vanlife
Energy usage:
2,000–4,000Wh per day
Recommended:
300–600Ah Lithium
Often combined with larger solar arrays and alternator charging.
For long-term travel considerations, see Full-Time Vanlife Energy Guide, coming soon.
Battery Capacity Examples
Example 1
Daily usage:
800Wh
Desired autonomy:
2 days
800 × 2
= 1,600Wh
Recommended:
150Ah Lithium
Example 2
Daily usage:
1,500Wh
Desired autonomy:
2 days
1,500 × 2
= 3,000Wh
Recommended:
250–300Ah Lithium
Example 3
Daily usage:
2,500Wh
Desired autonomy:
3 days
2,500 × 3
= 7,500Wh
Recommended:
600Ah Lithium or larger
Often paired with significant solar generation.
The Relationship Between Batteries and Solar
Battery capacity and solar generation must work together.
Large batteries with inadequate charging sources recharge slowly.
Large solar arrays with small batteries often waste available generation.
A balanced system typically provides the best performance.
As a rough guide:
| Battery Bank | Typical Solar Array |
| 100Ah Lithium | 150–250W |
| 200Ah Lithium | 300–500W |
| 300Ah Lithium | 500–700W |
| 400Ah+ Lithium | 700W+ |
These figures vary depending on travel style and climate.
Winter Battery Planning
Winter travel requires additional capacity.
Reasons include:
- Reduced solar generation
- Increased heating demand
- Longer nights
- More indoor device use
Many winter travellers discover that battery banks sized for summer become restrictive during colder months.
For detailed seasonal guidance, see upcoming Winter Vanlife Energy Strategies.
Common Battery Sizing Mistakes
Buying Batteries Before Calculating Usage
Always start with consumption.
Ignoring Winter Conditions
Winter places greater demands on most systems.
Assuming Bigger Is Always Better
Oversized systems increase costs and weight.
Underestimating Future Requirements
Energy needs often increase over time.
Forgetting Charging Capacity
Batteries are only useful if you can recharge them effectively.
Weight Considerations
Battery capacity affects vehicle payload.
Approximate weights:
100Ah AGM
25–30kg
100Ah Lithium
10–15kg
300Ah Lithium
30–45kg
Larger systems require careful payload planning.
This is particularly important for self-build campervans.
Battery Monitoring Is Essential
Even the best battery system benefits from accurate monitoring.
Good monitoring provides:
- State of charge information
- Consumption tracking
- Charging performance data
- Battery health indicators
Without monitoring, capacity planning becomes largely guesswork.
Recommended Battery Setups for 2026
Budget Touring Setup
- 100Ah Lithium
- 200W Solar
- DC-DC Charger
Popular Touring Setup
- 200Ah Lithium
- 400W Solar
- Smart Monitoring
Remote Work Setup
- 300Ah Lithium
- 600W Solar
- High-output DC-DC Charging
Full-Time Off-Grid Setup
- 400–600Ah Lithium
- 700W+ Solar
- Comprehensive Monitoring
These examples suit a wide range of UK travel styles.
Battery Capacity Planning Checklist
Before purchasing batteries:
- Calculate daily energy consumption
- Decide desired off-grid autonomy
- Add a safety margin
- Consider winter usage
- Assess charging methods
- Review payload capacity
- Plan for future expansion
A few calculations now can save significant money later.
Final Thoughts
The best battery size is not determined by trends, online opinions or what other travellers use.
It is determined by your own energy consumption and travel goals.
By calculating daily usage, understanding your desired autonomy and balancing battery capacity with charging capability, you can build a reliable electrical system that supports your adventures without unnecessary expense.
A properly sized battery bank provides confidence, flexibility and true off-grid independence, whether you’re exploring Scotland for a weekend or living on the road full-time.