A 200Ah battery does not have one fixed runtime. You also need its nominal voltage, usable energy, the loads you plan to run and any conversion losses. A small light and a large AC appliance draw on the same battery at very different rates.
Start with a planning calculation, then check the exact battery and inverter specifications. ROCKSOLAR’s 12V-class 200Ah LiFePO4 battery has 2,560Wh of nominal energy. The runtime examples below use explicit planning assumptions; they are not measured runtime tests or guaranteed hours of operation.
Convert amp-hours into energy
Nominal energy in watt-hours is nominal voltage multiplied by amp-hours. For ROCKSOLAR’s 12.8V nominal, 200Ah battery, the calculation is 12.8 × 200 = 2,560Wh, or 2.56kWh. A different nominal voltage changes the result, even when the amp-hour rating is unchanged.
Use the manufacturer’s confirmed nominal and usable-energy specifications for the product you choose. A retail “12V” category label is not a substitute for the battery’s rated voltage. Usable battery energy is also different from energy delivered to AC appliances.
Allow for discharge limits and inverter losses
For an illustrative runtime estimate, suppose the 2,560Wh battery is planned around 80% usable depth of discharge and an assumed 90% inverter efficiency. The simplified AC energy allowance is:
2,560Wh × 0.80 × 0.90 = 1,843.2Wh.
Both percentages are explicit example assumptions. Replace them with suitable information for the selected equipment and operating conditions. This simplified calculation does not separately account for inverter standby draw, changing efficiency, battery aging or temperature.
| Constant AC load | Example calculation | Approximate runtime |
|---|---|---|
| 100W | 1,843.2Wh ÷ 100W | 18.4 hours |
| 500W | 1,843.2Wh ÷ 500W | 3.7 hours |
| 1,000W | 1,843.2Wh ÷ 1,000W | 1.8 hours |
These rows compare energy use only. They do not establish that a particular battery and inverter can supply each load. For cycling appliances such as refrigerators, use an appropriate measured energy figure over time and check startup demand separately.
Check power delivery as well as runtime
Amp-hours describe charge capacity. Amps describe current. A 200Ah label does not mean the battery can supply any appliance that a large inverter will accept.
For illustration, a 3,000W AC load at an assumed 90% efficiency would require approximately 260A from a 12.8V DC source: 3,000 ÷ (12.8 × 0.90). Actual requirements vary with voltage and equipment. The battery, protection, wiring and inverter must all suit the proposed load; the runtime calculation alone cannot establish that.
Separate DC and AC loads
A DC appliance does not use the same conversion path as an AC appliance powered through an inverter. Make a list of both. Include the inverter’s own consumption where applicable, plus equipment such as communications devices that may remain on all day.
Also decide whether solar charging will be available during use. Daytime solar input can extend operation, but an overnight estimate should not assume charging from panels. Cloudy-weather reserve is a separate sizing decision.
Choose capacity around the actual job
If your essential loads use 1kWh each day, two days of reserve require 2kWh delivered to those loads before other allowances. Compare that requirement with confirmed usable energy. If your main concern is a large simultaneous load, check power limits first and ask whether a different system voltage or configuration is more suitable.
Review ROCKSOLAR’s 200Ah battery options and compare RV and cabin batteries. Send your requirements to ROCKSOLAR with your appliance wattages, hours of use, system voltage and inverter model.
Common questions
Will two batteries double runtime?
Available energy may increase with an approved configuration, but do not assume any batteries can be connected together. Confirm permitted series or parallel arrangements and the complete system design.
Can I use the table as a product guarantee?
No. It is a transparent arithmetic example. Final runtime depends on the selected equipment, actual loads and operating conditions.
