How Many Amp Hours Do You Need in a Campervan?
The single most important step in designing a campervan electrical system is calculating how many amp hours you actually consume each day. Most builds either over-specify (expensive) or under-specify (frustrating). Here is how to get it right.
Step 1: List your loads
Write down every electrical appliance in the van. For each one, find the wattage (on the label, data sheet, or product listing) and estimate how many hours per day you use it.
Common campervan loads:
| Appliance | Typical wattage | Daily hours |
|---|---|---|
| 12V compressor fridge (50L) | 40W average | 24 hours |
| LED lighting (full van) | 20–30W | 4 hours |
| 12V fan (e.g. MaxxAir roof vent) | 10–25W | 6 hours |
| Diesel heater (Webasto/Eberspacher) | 8–10W when running | 8 hours |
| Phone charging (2 phones) | 20W | 2 hours |
| Laptop | 30–65W | 4 hours |
| 12V water pump | 60–100W | 0.25 hours (brief use) |
| 12V TV (24") | 30–40W | 2 hours |
| Inverter (1,000W kettle, 3 min) | 1,000W | 0.05 hours |
| Inverter (laptop charger, 45W) | 50W effective | 4 hours |
Step 2: Convert to Watt-hours per day
For each appliance: Wh = Watts × Hours per day
Example daily consumption calculation:
| Appliance | Watts | Hours | Wh/day |
|---|---|---|---|
| Compressor fridge | 40W | 24 | 960Wh |
| LED lighting | 25W | 4 | 100Wh |
| Roof vent fan | 15W | 6 | 90Wh |
| Diesel heater (electrical) | 10W | 8 | 80Wh |
| Phone charging | 20W | 2 | 40Wh |
| Laptop | 45W | 4 | 180Wh |
| Water pump | 80W | 0.25 | 20Wh |
| Kettle (via inverter) | 1,100W | 0.05 | 55Wh |
| Total | 1,525Wh/day |
Step 3: Convert Wh to Ah
At 12V: Ah = Wh ÷ 12
In the example: 1,525Wh ÷ 12 = 127Ah/day
Step 4: Apply battery depth of discharge
You should not fully deplete your battery. The practical capacity you can use:
- LiFePO4: 90% usable DoD → divide required Ah by 0.9
- AGM: 50% usable DoD → divide required Ah by 0.5
Required battery capacity:
| Chemistry | Calculation | Battery needed |
|---|---|---|
| LiFePO4 | 127Ah ÷ 0.9 | 141Ah → buy 200Ah |
| AGM | 127Ah ÷ 0.5 | 254Ah → buy 2× 150Ah |
LiFePO4 wins significantly on battery size needed.
Step 5: Add a buffer for poor solar days
If you rely on solar, size the battery for 1–2 days of autonomy without sun. Multiply your daily Ah by 1.5–2.
In the example: 141Ah × 2 = 282Ah LiFePO4 minimum for 2-day autonomy.
Real-world sizing examples
Solo van lifer, UK, basic setup (fridge, lights, phone):
- Estimated daily: 70–90Ah
- LiFePO4 bank: 100Ah (provides ~1 full day, recharge via solar)
Couple, working from van (two laptops, fridge, lights, heating):
- Estimated daily: 130–170Ah
- LiFePO4 bank: 200Ah
Full-time family, hot climate (AC, full appliances):
- Estimated daily: 250Ah+
- LiFePO4 bank: 300–400Ah, or look at 24V system
The fridge is your biggest consumer — size it first
In most van builds, the compressor fridge accounts for 30–50% of daily consumption. Before choosing a battery, check the fridge's actual current draw from its data sheet. A quality compressor fridge (Engel, Dometic CFX, Brass Monkey) draws 25–50W average; a poorly insulated or underpowered fridge may draw more.
FAQ
What if I don't know how long I'll use each appliance?
Start with conservative estimates and monitor actual usage for a week using a battery monitor. Most people are surprised — the fridge draws far more than they expect, and lights draw far less.
Is bigger always better for battery capacity?
Bigger batteries cost more and weigh more. A correctly sized system with matched solar charging is better than an oversized battery that charges slowly from an undersized panel. Balance battery capacity with your charge sources.
How much solar do I need to match my daily consumption?
A rough rule: for every 100Ah daily consumption at 12V (1,200Wh), you need approximately 300–400W of solar in the UK summer, or 500–600W for reliable year-round charging. See our solar size calculator guide for a full calculation.