What Size House Battery Do You Need for a Van or RV?
Getting house battery sizing right means you're never stuck with a dead fridge — or carrying (and paying for) more battery than you'll ever use. Here's the formula US van and RV builders use.
Get your exact battery size
List your appliances and we'll calculate the watt-hours, Ah, and recommend a specific battery — free.
Step 1: Add up your daily watt-hours
List every appliance, its wattage, and hours of daily use, then multiply:
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| 12V compressor fridge | 50W (avg, cycling) | 24 | ~480 |
| LED lighting | 10W | 4 | 40 |
| Laptop charging | 60W | 2 | 120 |
| Phone charging | 10W | 3 | 30 |
| Water pump | 60W | 0.5 | 30 |
| Vent fan | 20W | 6 | 120 |
Total: ~820Wh/day for a modest setup. Full-timers running a CPAP, induction cooktop occasionally, or larger fridge often land at 1,500-2,500Wh/day.
Step 2: Convert to Ah
Battery Ah needed = daily Wh ÷ usable fraction ÷ battery voltage
For LiFePO4 (80% usable, 12.8V nominal):
820Wh ÷ 0.8 ÷ 12.8V ≈ 80Ah for one day of autonomy.
Step 3: Add a buffer for days without sun
Most builders size for 1.5-2 days of autonomy so a cloudy stretch doesn't leave you flat before solar or driving tops you back up:
80Ah × 1.5-2 ≈ 120-160Ah — round up to a common size like 100Ah or 200Ah.
Round up to the next common size
Battery capacities come in standard steps (100Ah, 150Ah, 200Ah, 300Ah). If your calculation lands at 160Ah, go to 200Ah — the extra headroom extends cycle life by reducing average depth of discharge, and gives you margin as you add gear.
Real-world examples
- Weekend van, no inverter: ~500-800Wh/day → 100Ah LiFePO4 (LiTime 100Ah, ~$220)
- Full-timer, fridge + laptop + occasional inverter use: ~1,200-1,800Wh/day → 200Ah LiFePO4 (LiTime 200Ah, ~$399)
- Heavy use, induction cooking, large fridge, CPAP: 2,000Wh+/day → 300-400Ah (two 200Ah in parallel, or a single 300Ah+ unit)
Don't forget charging
A bigger battery is only useful if you can refill it. Match your battery size to your charging plan — see the solar setup guide and charging systems guide so you're not stuck with a big bank that never gets back to full.