How big a battery bank do I need for RV solar?
The battery and the solar array answer two different questions. The array replaces what you use in one day. The battery carries you through the nights and the days when nothing replaces it. That is why the battery is sized by days, and the array by sun.
The formula our calculator uses
Battery Ah = daily Ah x days without charging / 0.85, rounded up to the next 50Ah, never below 100Ah.
- Daily Ah is everything you run in a day at 12V. Multiply by 12.8 for watt-hours.
- Days is how long you want to last if the sun and the alternator give you nothing.
- 0.85 is the usable share of a LiFePO4 battery the calculator plans on, leaving a reserve rather than running the bank to empty.
- Mains loads through an inverter are counted at 92% inverter efficiency, so a 120V load costs a little more from the battery than its label suggests.
What it gives for real rigs
These are the calculator's own presets, each at its default trip length:
| Rig preset | Daily use | Days | Battery |
|---|---|---|---|
| Travel trailer, propane fridge | 37Ah | 2 | 100Ah |
| Class C or Class A, 12V fridge | 59Ah | 2 | 150Ah |
| Fifth wheel, 12V fridge + laptop | 65Ah | 2 | 200Ah |
| Camper van, fridge + Starlink Mini | 69Ah | 2 | 200Ah |
| Off-road or teardrop, 12V fridge | 43Ah | 3 | 200Ah |
Three things that do and do not change the bank
- More days grows the battery and only the battery. The fifth wheel goes from 200Ah to 250Ah at three days. Its solar stays at 250W.
- Driving does not shrink the battery. A DC-DC charger reduces the solar the calculator asks for, but the bank is sized on the full daily use. You still need to get through the night, and through the days you do not drive.
- Air conditioning changes the order of magnitude. On top of the basic loads and a propane fridge, a 13,500 BTU rooftop unit running eight hours on a warm night takes a single day to about 6,964Wh and a 650Ah bank. Two hours on a mild evening needs 150Ah.
Check it against reality
The formula is only as good as the daily figure. A SmartShunt on the battery negative shows what you actually use, so after a weekend you can replace the estimate with a measurement and resize, or confirm you do not need to.
If you would rather carry the battery than wire it in, the Renogy 2-in-1 Smart PowerMax holds 1,280Wh and works as a 12V 100Ah house battery if you wire the rig later.
Run your own numbers in our RV solar & battery calculator, which applies this formula to the loads you tick.
What you need
Want the full walkthrough? Read the complete guide.