Battery Backup Calculator
Calculate the battery capacity needed for a target backup time, or estimate how long an existing battery bank can run your load. Works with 12 V, 24 V, 48 V and custom solar or inverter systems.
Calculate Battery Backup
Choose whether you want to size a new battery bank or estimate backup time from batteries you already have.
The battery-type preset only changes the starting usable-capacity assumption. Use the battery manufacturer's recommended operating limits for your actual battery.
Individual battery Ah is used only to estimate an approximate battery count. Series/parallel configuration must match the required bank voltage.
Enter the Ah capacity of the complete bank at the selected bank voltage. If you already know the bank's total Ah, keep quantity at 1.
How the Battery Backup Calculator Works
Battery sizing starts with the amount of AC energy your appliances need. The calculator then allows for inverter efficiency and the portion of the battery capacity you intend to use.
Battery Backup Time Formula
If you already own a battery bank, the reverse calculation estimates how long it may support an average AC load.
This is an energy-based planning estimate. High-current loads and battery characteristics can reduce real-world runtime.
12V, 24V and 48V Battery Systems
Battery bank voltage affects the amp-hour capacity required for the same amount of stored energy. A higher-voltage bank can provide the same watt-hour capacity at a lower Ah figure.
The calculator supports common 12 V, 24 V and 48 V systems plus a custom voltage field for other battery configurations.
Lithium vs Lead-Acid Battery Backup
Lithium and lead-acid batteries can have different recommended usable capacity ranges. This calculator provides editable starting assumptions instead of permanently fixing one depth-of-discharge percentage.
Always use the operating limits specified for the exact battery model, especially for lithium systems managed by a BMS.
Battery Backup Calculator for Pakistan & India
The energy formulas are not country-specific, so the same calculator can be used for homes, offices and solar systems in Pakistan and India. Enter the actual appliance load, battery voltage and manufacturer-recommended usable capacity.
Frequently Asked Questions
How do I calculate battery backup time?
Convert the battery bank capacity to watt-hours, multiply by the usable depth of discharge and inverter efficiency, then divide by the average AC load.
How do I calculate the Ah battery I need?
First calculate the watt-hours required for your desired backup time. Adjust for inverter losses and usable battery capacity, then divide by battery-bank voltage to estimate Ah.
Why does battery voltage matter?
Watt-hours equal volts multiplied by amp-hours. For the same stored energy, a higher-voltage battery bank requires fewer amp-hours.
Why is depth of discharge editable?
Different battery chemistries and manufacturers specify different usable operating ranges. An editable field avoids treating all batteries as identical.
Does this calculator include inverter losses?
Yes. Inverter efficiency is an editable input and is included in both battery-sizing and backup-time calculations.
Can I use this for a solar inverter?
Yes. It can provide an initial battery-energy estimate for solar and inverter systems, but final configuration should follow equipment and battery specifications.