Security and low voltage
Battery backup energy runtime
Estimate constant-load backup duration from supplied battery energy and real-watt loads.
Your inputs
Complete the fields for your selected method. Zero means intentionally zero, not unknown. Currency selection labels amounts; it does not convert exchange rates.
How this calculation works
usable delivered energy = nominal Wh × usable share × conversion efficiency; runtime hours = delivered Wh/real load W
This is an energy-budget estimate, not a UPS manufacturer runtime curve. Battery chemistry, age, temperature, discharge rate, cutoff limits and transient loads can change actual runtime. Use real watts, not VA. Usable share and efficiency are supplied assumptions, not safety recommendations or a backup guarantee. Use your own records for the same scope and period. Example figures are illustrative, not industry benchmarks. Results exclude income taxes and any cost you have not entered. Check the result before pricing work or committing resources.
What information do I need?
Use records for the same job, equipment or accounting period. Only the fields for your selected entry method are required. An unknown amount is not zero.
Input definitions and where to find them
- Battery energy entry: Choose the entry method matching the information you have. Only its active inputs are required.
- Nominal battery energy (Wh): Use the matching measured quantity, time log, schedule or clearly stated estimate. Zero means intentionally none; an unknown amount is not zero. Used with: Known nominal watt-hours.
- Nominal battery voltage (V): Use the matching measured quantity, time log, schedule or clearly stated estimate. Zero means intentionally none; an unknown amount is not zero. Used with: Nominal voltage and amp-hour rating.
- Battery amp-hour rating on same basis (Ah): Use the matching measured quantity, time log, schedule or clearly stated estimate. Zero means intentionally none; an unknown amount is not zero. Used with: Nominal voltage and amp-hour rating.
- Usable nominal-energy share from your scenario (%): Enter a percentage from your records or an explicitly chosen scenario. No typical or recommended rate is supplied.
- Supplied conversion efficiency (%): Enter a percentage from your records or an explicitly chosen scenario. No typical or recommended rate is supplied.
- Real electrical loads: Enter matching rows from your records; add or remove rows as needed.
- Device group: Use the matching measured quantity, time log, schedule or clearly stated estimate. Zero means intentionally none; an unknown amount is not zero.
- Combined real power for this group (W): Use the matching measured quantity, time log, schedule or clearly stated estimate. Zero means intentionally none; an unknown amount is not zero.
Use the Where to find this value controls beside the inputs for available work-it-out helpers. Estimates remain your assumptions; a helper does not verify the source figures.
Worked example
Example amounts use US dollars (USD).
Example answer: Ideal constant-load runtime is 7.20 hours for the illustrative inputs below.
Example inputs
- Battery energy entry: Known nominal watt-hours
- Nominal battery energy: 1,000.00 Wh
- Usable nominal-energy share from your scenario: 80.00 %
- Supplied conversion efficiency: 90.00 %
- Real electrical loads
- Device group: Devices
- Combined real power for this group: 100.00 W
- Ideal constant-load runtime
- 7.20 hours
- Modeled usable delivered energy
- 720.00 Wh
- Combined real load
- 100.00 W
These illustrative values are not recommended rates or industry averages. Replace every example input with your own figures.
Use the result well
Estimate constant-load backup duration from supplied battery energy and real-watt loads. Inputs come from your own records and stated assumptions; no rates or legal limits are looked up.
Keep inputs on the same scope and time basis. Calculations retain precision internally; displayed values generally round to two decimal places, with extra precision for very small values and whole-unit rounding where required. Economic comparisons describe your supplied assumptions and do not guarantee future results.
This tool provides business arithmetic. It does not approve engineering designs, establish legal or tax treatment, select equipment or certify safe operating conditions.