This calculator is built specifically for 12-volt systems — the most common battery voltage for RVs, boats, camping setups, and off-grid solar. Voltage is locked at 12V so you just enter capacity, load, and your battery type's safe discharge depth.
Common 12V Load Reference
| Device | Typical Watts | Runtime on 100Ah (80% DoD) |
|---|---|---|
| LED light strip (1m) | 5-15W | 57-172 hours |
| Phone charger | 10-18W | 48-86 hours |
| Laptop charger | 45-65W | 13-19 hours |
| 12V compressor fridge | 30-60W avg | 14-28 hours |
| CPAP machine | 30-60W | 14-28 hours |
| Portable fan | 15-40W | 21-57 hours |
| Water pump (RV) | 40-100W | 8.5-21 hours |
| Inverter + TV (32") | 50-80W | 10-17 hours |
Runtimes above assume a 100Ah 12V battery at 80% DoD and 90% system efficiency. Your actual results will differ based on battery chemistry, age, and temperature.
Example: Weekend Camping with a 12V Battery
Scenario: you are car camping for two nights with a 100Ah LiFePO4 battery. Your nightly load looks like this:
- LED lights — 10W for 5 hours = 50Wh
- Phone charging (2 phones) — 20W for 3 hours = 60Wh
- 12V fridge — 40W average for 24 hours = 960Wh (over the full weekend)
- Portable speaker — 5W for 6 hours = 30Wh
Total weekend energy: 50 + 60 + 960 + 30 = 1,100Wh over two days. Your 100Ah 12V LiFePO4 battery stores 1,200Wh total, with 960Wh usable at 80% DoD. That is not enough — you are 140Wh short.
Options: bring a second battery, add a 100W portable solar panel (which produces roughly 400-500Wh per day in decent sun), or reduce fridge time by pre-cooling food in a good cooler.
Frequently Asked Questions
Recharging with solar? Our <a href="/solar/solar-battery-charge-time-calculator">solar battery charge time calculator</a> shows how long your panels take to refill a 12V battery.
A 12V system is the simplest and most versatile battery setup for portable and mobile use. Match your battery capacity to your actual load — not your worst-case fantasy load — and you will avoid both overspending and running out of power at 2 AM.
Last updated:
Written and maintained by Dan Dadovic, Developer & Off-Grid Energy Enthusiast. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, and wind power — all from building and maintaining his own systems..
Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.