Calculate inverter backup time from battery Ah, battery voltage, appliance load and inverter efficiency. Estimate runtime for 50Ah, 150Ah and 180Ah batteries, including two-battery systems.
Enter your actual battery and appliance details for a more useful estimate.
Enter the total wattage of appliances running together. Use actual input watts, not only marketing labels.
Calculated from your battery bank and appliance load.
Enter your settings to calculate estimated backup time.
Wondering how long your home inverter battery will run during a power cut? Our inverter battery backup calculator helps estimate backup time based on battery capacity, voltage, appliance load and inverter efficiency. Whether you use a 50Ah, 100Ah, 150Ah, 180Ah or 200Ah battery, enter your system details to get an estimated runtime.
This online inverter battery backup time calculator is designed for home users, shop owners, offices and anyone planning a battery-based backup system. You can calculate estimated runtime for a single battery or a compatible multiple-battery bank, compare appliance loads and estimate the battery capacity needed for your desired backup duration.
Use the calculator to understand your expected power backup before purchasing a new battery, upgrading your inverter or deciding which appliances to run during an outage. The result is an estimate rather than a guaranteed backup time because real performance depends on battery condition, discharge rate and equipment specifications.
An inverter battery backup calculator estimates how long a battery-powered inverter can supply electricity to connected appliances. It uses the battery bank's nominal energy, the usable portion of that energy, inverter conversion efficiency and the total running load.
Instead of guessing how many hours a battery will last, a battery backup calculator for inverter helps you compare different battery capacities and appliance combinations using consistent assumptions.
Estimate the number of hours your battery can support a selected appliance load.
Compare 50Ah, 100Ah, 150Ah, 180Ah and other battery sizes.
Estimate the energy in compatible series and parallel battery configurations.
Estimate battery capacity for a target runtime and your connected load.
Follow these steps to calculate the estimated runtime of your inverter battery.
Choose the nominal voltage printed on your battery, such as 12V or 24V. If several batteries are connected in series, the total bank voltage increases. Make sure the selected configuration matches the inverter's supported DC input voltage.
Enter the ampere-hour (Ah) rating of one battery. Common home inverter batteries include 100Ah, 120Ah, 150Ah, 180Ah and 200Ah models. If your batteries have different capacities, do not assume they can safely be combined; follow the manufacturer's installation guidance.
Choose the total number of batteries and how many are connected in series in each string. Series-connected batteries increase voltage while maintaining the Ah rating of each string. Parallel-connected strings increase total Ah capacity while maintaining the string voltage. Use only configurations supported by the inverter and battery manufacturer.
Select tubular lead-acid, flat-plate lead-acid or lithium, as applicable. Set a usable discharge percentage appropriate for the battery's specifications and desired service life. A higher usable discharge setting can increase estimated runtime but may not be suitable for every battery.
Enter the combined running wattage of the appliances expected to operate at the same time. You can also build an estimated load using fans, lights, a television and other appliances. Use actual power consumption figures where possible.
Inverter efficiency represents the proportion of DC energy that becomes usable AC energy. If your inverter manufacturer provides an efficiency figure, use that value. Efficiency can change with the load, operating mode and inverter design.
The calculator displays estimated backup time, nominal battery energy, usable AC energy, approximate DC current and a suggested battery capacity for your target runtime. Check inverter power limits and appliance starting surges before relying on the estimate.
The basic energy calculation starts with the battery bank's nominal voltage and ampere-hour capacity. The calculator then applies usable discharge and inverter efficiency before dividing the estimated usable energy by the appliance load.
For example, if a battery bank has 1,800Wh of nominal energy, the selected usable discharge is 50%, inverter efficiency is 85% and the load is 300W:
This is a simplified energy-based estimate. Lead-acid batteries can deliver less usable capacity at high discharge rates, and actual runtime can be reduced by battery age, temperature, inverter idle consumption, wiring losses and voltage cut-off settings.
A 150Ah battery backup time calculation depends on the battery voltage, usable discharge, inverter efficiency and appliance load. The following examples assume a 12V battery, 50% usable discharge and 85% inverter efficiency.
| Running load | Estimated backup time | Example use |
|---|---|---|
| 100W | About 7.65 hours | Light appliance load |
| 200W | About 3.83 hours | Small home load |
| 300W | About 2.55 hours | Several light appliances |
| 500W | About 1.53 hours | Higher running load |
| 750W | About 1.02 hours | Heavy load for this example |
These estimates are based on 12V × 150Ah = 1,800Wh of nominal energy. Actual backup may be lower, particularly at high loads. Always check battery specifications and the inverter's operating limits.
A 180Ah battery backup time calculator uses the same basic formula but starts with a larger nominal capacity than a 150Ah battery at the same voltage. Under identical assumptions, a 12V 180Ah battery has 2,160Wh of nominal energy.
| Running load | Estimated backup time |
|---|---|
| 100W | About 9.18 hours |
| 200W | About 4.59 hours |
| 300W | About 3.06 hours |
| 500W | About 1.84 hours |
| 750W | About 1.22 hours |
These examples assume 50% usable discharge and 85% inverter efficiency. They are estimates, not guaranteed performance figures. The calculator above lets you change the load and battery settings to suit your system.
A 50Ah battery has less stored energy than a larger battery at the same voltage, so its backup duration is generally shorter for the same load and discharge settings. Small-capacity batteries may be suitable for compatible low-power systems, but confirm the inverter's minimum battery capacity, voltage and current requirements.
Use the 50Ah battery backup time preset to calculate estimated runtime for your actual appliance load. Do not rely on battery capacity alone: a 50Ah battery at 24V has a different nominal energy level from a 50Ah battery at 12V.
A 2 battery inverter backup calculation must account for how the batteries are connected. Two batteries connected in series increase the bank voltage while retaining the Ah rating of the string. Two identical batteries connected in parallel retain the voltage and approximately double the Ah capacity.
| Configuration | Bank voltage | Bank capacity | Nominal energy |
|---|---|---|---|
| One 12V 150Ah battery | 12V | 150Ah | 1,800Wh |
| Two 12V 150Ah in series | 24V | 150Ah | 3,600Wh |
| Two 12V 150Ah in parallel | 12V | 300Ah | 3,600Wh |
Series and parallel arrangements can have the same nominal total energy when identical batteries are used, but they operate at different bank voltages and current levels. The inverter must support the actual bank voltage. Never connect a battery bank in a configuration that conflicts with the inverter or battery manufacturer's instructions.
A 2kVA inverter backup time calculation needs both the battery bank and the connected load. The 2kVA rating describes apparent power, not battery energy or a fixed number of backup hours. Real-power capability depends on the inverter's specified power factor and continuous watt rating.
For instance, an inverter with a 2,000VA rating and a rated power factor of 0.8 would correspond to 1,600W of real power under that rating assumption. This does not mean it can operate at that load for a particular duration: runtime still depends on the battery bank, usable discharge and conversion losses. Check the actual product specification and surge rating.
Tubular lead-acid batteries are commonly used in home inverter systems. Their backup time depends on the rated capacity, charging condition, battery age, temperature, load and permitted depth of discharge.
Our tubular battery backup calculator can estimate runtime by using the battery's voltage and Ah rating alongside a suitable usable-discharge setting. Follow the manufacturer's guidance for discharge limits and charging. A higher discharge depth can increase estimated runtime but may reduce service life.
For a home inverter, first identify which appliances must run during a power cut. Add their actual running wattages, then consider whether motors, refrigerators or pumps introduce high starting surges. The total running load should remain within the inverter's real-power rating, and starting loads must be supported by its surge capability.
Fans, LED lights, routers and televisions often make up a smaller load than heating appliances or large motors, but actual consumption varies by model. Use measured watts or the appliance specification rather than assuming every appliance has a fixed power requirement.
With the home inverter backup time calculator, compare different combinations of appliances and see how reducing the load can affect the estimated runtime.
A solar inverter or hybrid inverter may use solar panels, batteries and grid power in different operating modes. Battery backup during a power cut depends on the inverter's supported backup function, battery bank and connected load. Solar generation can change the result during daylight, but it should not be assumed to remain constant throughout the outage.
For a battery-only runtime estimate, use the calculator above with the battery bank details and the load supplied by the inverter. For a full solar-system estimate, also account for solar generation, weather, charge controller limits and the manufacturer's system configuration.
Multiply nominal battery voltage by bank Ah to estimate watt-hours. Multiply that energy by the usable discharge fraction and inverter efficiency, then divide by the connected running load in watts. Actual runtime can differ due to discharge rate, battery condition and inverter losses.
It depends on the battery voltage, usable discharge, inverter efficiency and load. Under an illustrative 12V, 50% discharge and 85% efficiency assumption, a 150Ah battery supplying 300W has an energy-based estimate of approximately 2.55 hours.
A 12V 180Ah battery has 2,160Wh of nominal energy. Under the same illustrative 50% discharge and 85% efficiency assumptions, a 300W load gives an energy-based estimate of approximately 3.06 hours.
Enter the battery voltage, 50Ah capacity, usable discharge, inverter efficiency and total load. The calculator will estimate runtime. A 50Ah battery's backup time cannot be determined accurately from Ah alone.
Not necessarily. kVA describes an inverter's apparent power rating, not its stored battery energy. Backup time depends on the battery bank's usable energy and the actual load, and the connected load must remain within the inverter's supported limits.
Two identical batteries can approximately double nominal stored energy compared with one battery, when connected in a compatible configuration. Actual runtime depends on load, discharge settings, efficiency and battery condition. The inverter must support the resulting bank voltage.
A simplified formula is: backup hours = nominal battery-bank Wh × usable-discharge fraction × inverter efficiency ÷ load watts. It is an estimate because real battery capacity changes with discharge rate and operating conditions.
Tubular batteries are a common option for home inverter systems. Suitability depends on the required capacity, cycling needs, charging system, maintenance requirements and manufacturer specifications. Compare products using their documented ratings and intended use.
Yes, for an estimate of battery-only runtime if the solar or hybrid inverter supports the chosen battery configuration. Solar generation during the outage is not included in this simplified battery-only calculation.
Possible causes include an aged or incompletely charged battery, high discharge current, lower actual usable capacity, inverter idle consumption, wiring losses, temperature, high appliance load or starting surges. Check the battery and inverter specifications and actual load.
Yes. Select the required-capacity mode, enter the desired backup duration and running load, and set the battery and inverter assumptions. The result is an estimated capacity requirement; select a supported battery configuration with appropriate margin.
Yes. The calculator is designed to estimate backup time and battery capacity directly in your browser without requiring a paid calculation service.
Use the calculator above to estimate backup duration for your battery and appliance load. Compare battery capacities, check a compatible multiple-battery configuration and plan the runtime you need. For the most useful estimate, use the actual battery rating, inverter efficiency and appliance power consumption.