Battery Capacity for RV Solar: How Much Do You Need?
Power (watts) and energy (watt-hours) answer different questions. A battery can be rated for plenty of power — enough watts to run everything at once — and still run out of energy in a few hours if its capacity doesn't match how much you actually use per day. This guide is about that second number.
Watts vs. watt-hours, quickly
- Watts measure how much power something draws right now.
- Watt-hours (Wh) measure total energy used over time — watts × hours.
A 100W light left on for 5 hours uses 500Wh. A battery's capacity (its "tank size") is rated in Wh (or sometimes Ah at a given voltage, which converts to Wh) — compare your daily Wh use against that capacity, not against your peak wattage.
Step 1: Estimate your daily watt-hour use
For each appliance you'll run, multiply its running watts by how many hours per day you actually run it, then add them up. Worked example:
| Appliance | Running watts | Hours/day | Watt-hours |
|---|---|---|---|
| Refrigerator (cycles on/off) | 400 W | ~6 effective hrs | 2,400 Wh |
| Lights + charging | 100 W | 4 hrs | 400 Wh |
| Water pump | 50 W | 1 hr | 50 Wh |
| Laptop/devices | 60 W | 3 hrs | 180 Wh |
| Total | ~3,030 Wh/day |
(Air conditioning is usually left out of this table and run from shore power or a dedicated generator, since its daily Wh use is large and climate-dependent — if you're running AC off battery, add its own running-watts × hours-per-day line.)
Step 2: Add a buffer
A common rule of thumb is recommended battery capacity = daily Wh use × 1.5. That buffer covers cloudy/low-sun days when solar recharge falls short, and avoids regularly draining the battery down to near empty, which shortens most battery chemistries' lifespan. Using the example above: 3,030 × 1.5 ≈ 4,550 Wh recommended capacity.
Step 3: Translate to a real product spec
Battery capacity is often listed in Wh directly, or in Ah (amp-hours) at a stated voltage — multiply Ah × V to get Wh (e.g., a 100Ah 12V battery ≈ 1,200Wh). Compare apples to apples before buying.
Typical range for RV use
For most RV setups — not full-time off-grid living with heavy AC use, more like weekend/moderate use — 2,000–3,000 Wh of battery capacity is a commonly cited comfortable range. Heavier daily use (working remotely, running more appliances, longer trips without shore power) pushes that higher; light use (mostly lights, charging, a fridge) can get by with less.