"How many batteries do I need?" is the most common question we get asked. The answer isn't "one" or "two" - it's about total capacity in amp-hours (Ah) based on your actual power consumption.
This guide will help you calculate exactly how much battery capacity you need, whether you're a weekend camper or full-time van lifer. We'll cover the simple formula, real-world examples, and why most people overestimate their needs.
Quick Answer
Weekend use: 100Ah lithium battery
Regular camping (with fridge): 200-230Ah lithium
Full-time living: 300-400Ah+ lithium
The Simple Calculation
Battery Size Formula
Battery Capacity = (Daily Usage × Days Autonomy) ÷ Battery Voltage
Then add 20-30% buffer for battery health
Daily Usage: Total watt-hours (Wh) you use per day
Days Autonomy: How many days without charging
Battery Voltage: Usually 12V for campervans
Example Calculation
Let's say you use 400Wh per day and want 2 days autonomy:
(400Wh × 2 days) ÷ 12V = 66.6Ah minimum
Add 30% buffer: 66.6 × 1.3 = 87Ah
✓ Choose 100Ah battery (next size up)
Step 1: Calculate Your Daily Usage
List every electrical device you'll use and estimate daily watt-hours (Wh). Here's a comprehensive list of common campervan loads:
Essential Loads
- • LED lights (4 × 3W × 3 hours) = 36Wh
- • Water pump (5 min/day × 4A) = 4Wh
- • Phone charging (2 phones) = 20Wh
- • USB fan (5W × 6 hours) = 30Wh
Total: ~90Wh/day
Big Power Users
- • 12V Compressor Fridge = 300-500Wh
- • Laptop (8 hours work) = 50-100Wh
- • Diesel heater (winter) = 30-60Wh
- • Inverter (TV, hairdryer) = varies widely
Fridge alone = 30-50% of usage
The Fridge Reality Check
A 12V compressor fridge is by far your biggest power drain. If you're running a fridge, you need at least 200Ah lithium for comfortable multi-day autonomy. Without a fridge, 100Ah is often plenty.
Real-World Usage Examples
Weekend Warrior
1-2 nights, minimal power use
Typical Daily Loads
- • LED lights - 10Wh/day
- • Phone charging - 20Wh/day
- • Water pump - 5Wh/day
- • USB fan - 15Wh/day
Recommended Battery
100Ah lithium (1200Wh usable)
Plenty of buffer for unexpected use, won't need daily charging
Regular User
3-5 nights, moderate power use
Typical Daily Loads
- • LED lights - 20Wh/day
- • Phone/tablet charging - 40Wh/day
- • 12V fridge - 300Wh/day
- • Laptop charging - 50Wh/day
- • Water pump - 10Wh/day
Recommended Battery
200-230Ah lithium (2400-2760Wh usable)
2+ days autonomy without charging, comfortable power headroom
Full-Time Van Lifer
Off-grid living, heavy power use
Typical Daily Loads
- • LED lights - 30Wh/day
- • Phone/laptop - 100Wh/day
- • 12V fridge - 400Wh/day
- • Diesel heater - 50Wh/day
- • Inverter loads (TV, etc) - 200Wh/day
- • Water pump - 15Wh/day
Recommended Battery
300-400Ah lithium (3600-4800Wh usable)
Multiple days autonomy, handles cloudy weather, supports high-power appliances
Lithium vs Lead-Acid: The Capacity Difference
Lithium (LiFePO4)
- 100% usable capacity
- 100Ah = 1200Wh usable power
- No voltage drop under load
- 3000+ charge cycles
Example: 200Ah lithium = 2400Wh usable
Lead-Acid / AGM
- •Only 50% usable capacity
- •100Ah = 600Wh usable power
- •Voltage drops significantly at 50%
- •300-500 charge cycles
Example: 200Ah lead-acid = 1200Wh usable
Key Takeaway
You need half the rated Ah capacity with lithium compared to lead-acidfor the same usable power. Plus lithium is 50% lighter, lasts 5-10x longer, and charges faster. That's why we only install lithium batteries in modern campervan conversions.
Factor in Solar Charging
Solar panels dramatically reduce the battery capacity you need because they're constantly topping up. Here's how solar changes the equation:
Without Solar
Battery must store enough for multiple days between driving or hookup.
400Wh daily × 3 days = 1200Wh needed
= 200Ah lithium minimum
With Solar (200W)
Solar generates 600-1000Wh/day in summer, battery is just for nighttime buffer.
400Wh daily - 800Wh solar = surplus!
= 100Ah lithium sufficient
Our Recommendation
We recommend 200W+ solar with 200Ah lithium for most campervan users. This gives you genuine off-grid freedom in summer and 2-3 days autonomy in winter. It's the sweet spot between cost and capability.
Common Battery Sizing Mistakes
❌ "I'll just get a massive battery"
Problem: Large battery capacity is useless if you can't charge it. A 400Ah battery with no solar in UK winter will take 2-3 days of driving to fully charge. Better to match battery size to your charging capability (solar/driving).
❌ "One battery should be enough"
Problem: If you're thinking in terms of "number of batteries" rather than total Ah capacity, you haven't done the calculation right. Modern lithium batteries come in various capacities (100Ah, 230Ah, etc). Focus on total capacity needed, not number of units.
❌ "Lead-acid is cheaper"
Problem: Initial cost maybe, but you need double the capacity, they're heavier, last 1/5th as long, and need replacing every 3 years. Over 10 years, lithium is significantly cheaper per Wh delivered. Plus you avoid the hassle of battery replacements.
❌ "I don't need to calculate"
Problem: Guessing leads to either overspending on capacity you'll never use, or undersizing and running out of power constantly. Spend 30 minutes calculating your actual usage - it's worth it.
Professional Battery Installation
We'll help you calculate the exact battery capacity you need, recommend the right lithium battery for your budget, and install it safely with proper cabling, fusing, and battery monitoring. Every installation includes:
- Free power consumption consultation
- Premium lithium batteries (Fogstar, Victron)
- Correctly sized cables and fusing
- Battery monitor installation
- Full system testing
- Warranty registration