Inverter Battery Runtime Calculator
What the Inverter Battery Runtime Calculator does
The Inverter Battery Runtime Calculator estimates how long a battery bank can supply power to devices connected through an inverter. It uses the battery bank’s voltage and capacity, the portion of capacity you plan to use, the inverter’s efficiency, and the average power drawn by your devices.
The result, labeled Estimated Runtime, is shown in hours. It can help you plan for a power outage, a camping trip, or an off-grid setup where you want to run AC devices from a battery. The calculator assumes a steady average load and starts with illustrative default values, so replace them with figures that fit your equipment.
Treat the result as a planning estimate. Battery age, temperature, discharge rate, inverter power consumption, and changes in the connected load can all affect how long your equipment actually runs.
How to use the Inverter Battery Runtime Calculator
Enter the following five values to estimate runtime:
- Battery bank voltage (V): Enter the nominal voltage of the complete battery bank. The calculator accepts values from 6 to 48 volts.
- Battery bank capacity (Ah): Enter the total amp-hour capacity of the battery bank at its configured voltage. The accepted range is 1 to 10,000 Ah.
- Usable depth of discharge (%): Enter the percentage of battery capacity you plan to use. The calculator accepts 10% to 100%. Check the battery manufacturer’s guidance when choosing this figure.
- Inverter efficiency (%): Enter the estimated percentage of battery energy the inverter converts into usable AC energy. The accepted range is 50% to 100%.
- Average connected load (W): Enter the average combined power consumption of the devices you expect to run, in watts. The calculator accepts 1 to 10,000 W.
Once you enter the values, read the Estimated Runtime in hours. For example, a result of 2.50 hours represents approximately two hours and 30 minutes. The displayed result is rounded to two decimal places.
Use the capacity of the complete bank, not the sum of individual battery ratings without considering how the batteries are connected. For example, two identical 12 V, 100 Ah batteries connected in series form a 24 V, 100 Ah bank. Connected in parallel, they form a 12 V, 200 Ah bank. Follow the equipment manufacturer’s instructions when configuring a battery bank.
How the Inverter Battery Runtime Calculator formula works
The calculator first estimates the battery bank’s nominal energy in watt-hours. It then applies the usable depth of discharge and inverter efficiency before dividing by the average connected load:
Estimated runtime (hours) = Battery bank voltage (V) × Battery bank capacity (Ah) × (Usable depth of discharge ÷ 100) × (Inverter efficiency ÷ 100) ÷ Average connected load (W)
Multiplying volts by amp-hours gives an estimate of the bank’s nominal watt-hours. The depth of discharge reduces that figure to the portion you intend to use. Inverter efficiency accounts for some energy lost during conversion from battery power to AC power. Dividing the remaining watt-hours by watts gives an estimated number of hours.
Worked example using the default inputs
Assume a 12 V battery bank with a 100 Ah capacity, a usable depth of discharge of 50%, an inverter efficiency of 85%, and a constant average load of 500 W. These percentages and the load are illustrative assumptions.
- Nominal battery energy: 12 V × 100 Ah = 1,200 Wh.
- Energy within the assumed usable depth of discharge: 1,200 Wh × 0.50 = 600 Wh.
- Estimated AC energy after inverter conversion: 600 Wh × 0.85 = 510 Wh.
- Estimated runtime: 510 Wh ÷ 500 W = 1.02 hours.
The default result is therefore 1.02 hours, or approximately one hour and one minute. Actual runtime may be shorter or longer because the calculation does not model every loss or change in battery performance.
Use cases for the Inverter Battery Runtime Calculator
An inverter battery runtime calculator is useful whenever you need a rough idea of how long a battery-powered inverter can support an average load.
- Power outage planning: Estimate how long a battery bank might run selected lights, communication equipment, or other modest AC loads.
- Camping and road trips: Compare the effect of different device loads on a portable battery and inverter setup.
- Off-grid equipment: Estimate operating time for devices powered from a dedicated battery bank between charges.
- Comparing battery bank sizes: Change the bank capacity to see how additional storage affects the estimate while keeping the other assumptions the same.
- Reducing power consumption: Compare different average loads to see how using fewer devices or lower-power equipment could extend runtime.
For readers considering vehicle batteries, check that the battery is appropriate for the intended use. A battery designed primarily for starting an engine may have different discharge guidance from a battery intended for repeated deep cycling. Consult the manufacturer before choosing an allowable depth of discharge.
Other factors to consider when calculating Estimated Runtime
Discharge rate: A battery’s stated amp-hour capacity is measured under specified conditions. At a high discharge rate, particularly with some lead-acid batteries, the capacity available in practice can be lower than the nominal rating. A large inverter load may therefore run for less time than the formula suggests.
Battery condition and temperature: Aging, incomplete charging, and temperatures outside the battery’s preferred operating range can reduce available capacity. The calculator does not adjust for these conditions. Use a capacity figure appropriate to the battery’s condition where reliable information is available.
Inverter idle consumption: An inverter can draw power even when connected devices are using little or no power. The formula does not separately account for this idle consumption. Manufacturer specifications and measured power use can help you make a more realistic estimate.
Changing loads: Many appliances do not draw the same power continuously. A device may cycle on and off or use more power at certain times. Enter an estimated average load for the period you want to measure, including the devices you expect to operate together.
Starting power and equipment limits: Some devices briefly need more power when they start than they use during normal operation. A favorable runtime estimate does not establish whether the inverter, battery, cables, or protection equipment can handle that demand. Check the relevant equipment specifications separately.
Battery cutoff: An inverter or battery management system may stop operation when voltage falls to its cutoff point. This can happen before the energy implied by the simple calculation has been delivered, especially under a heavy load.
Inverter battery runtime calculator FAQ
How long will a 12 V, 100 Ah battery run an inverter?
It depends on the usable depth of discharge, inverter efficiency, and average load. With the calculator’s illustrative defaults of 50% usable depth of discharge, 85% inverter efficiency, and a 500 W load, the estimate is 1.02 hours. Different assumptions produce a different result.
What depth of discharge should I enter?
Enter the percentage of the battery bank’s capacity you plan to use, guided by the battery manufacturer’s recommendations and your intended use. The default 50% is an illustrative assumption; it is not a universal recommendation for every battery type.
Does a larger inverter make the battery last longer?
Increasing an inverter’s power rating alone does not increase battery capacity. Runtime depends on the energy available from the battery, the actual average load, and the inverter’s efficiency and consumption. Choose equipment with suitable ratings for the devices you intend to run.
How do I find the average connected load?
Check the power information for each device and estimate how much power the devices use together over the period of interest. If a device cycles on and off, its average consumption can differ from its power draw while running. A suitable power meter can help you measure actual usage.
Does the calculator include inverter idle power?
No. The formula applies the entered efficiency percentage, but it does not separately model inverter idle consumption. It also does not account for battery aging, temperature, high discharge rates, or changing loads, so allow for those limitations when planning.