Battery Autonomy Calculator
How many hours of backup does the existing bank give?
Your numbers
Your results
Battery Autonomy Calculator by TheCalcTools
How the Battery Autonomy Calculator works
Enter the bank’s rated Ah and voltage and its current state of health.
Usable energy is rated energy × DoD × efficiency × health.
Backup time is usable energy divided by load.
The formula
Worked example
Using the default values shown in the calculator:
| Bank capacity (Ah) | 400 |
|---|---|
| Bank voltage (V) | 48 |
| Usable depth of discharge (%) | 80 % |
| Efficiency (%) | 95 % |
| Battery health (% of rated capacity) | 85 % |
| Load (watts) | 3000 |
- Usable energy = 400 × 48 × 0.80 × 0.95 × 0.85 = 12.40 kWh.
- At 3 kW the bank lasts 4.13 hours (248 minutes).
Result:
| Usable energy (kWh) | 12.40 |
|---|---|
| Backup time (hours) | 4.13 |
| Backup time (minutes) | 248 |
Frequently asked questions
What if my load is in amps?
Multiply amps by bank voltage to get watts, or use the DC load current calculator.
Is discharge rate considered?
Not here. At high discharge rates (short autonomy), lead-acid delivers less than its rated Ah, so real runtime can be shorter. Use the manufacturer’s discharge tables.
Sources and further reading
Related calculators
More in Telecom Power & Passive Infrastructure · All calculators
This calculator gives estimates for planning only. Electrical installations must be designed, checked and carried out by qualified personnel following local codes and the equipment manufacturer's data. Never rely on this result alone for safety-critical decisions. See our disclaimer.