Telecom Battery Bank Sizing Calculator (48V)
How many Ah do you need to keep the site up for a given outage?
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Telecom Battery Bank Sizing Calculator (48V) by TheCalcTools
How the Telecom Battery Bank Sizing Calculator (48V) works
Enter the DC load in watts, the hours of autonomy and the bank voltage.
Enter usable depth of discharge, converter efficiency, temperature derating and an ageing margin.
Ah = energy needed ÷ (voltage × usable factors) × margin.
The formula
Worked example
Using the default values shown in the calculator:
| Load (watts) | 3000 W |
|---|---|
| Autonomy required (hours) | 4 |
| Nominal bank voltage (V) | 48 |
| Usable depth of discharge (%) | 80 % |
| Inverter/converter efficiency (%) | 95 % |
| Temperature derating (0.8–1.0) | 0.95 |
| Ageing/design margin (%) | 25 % |
| Battery module size (Ah at bank voltage) | 100 |
- Ah = 3,000 × 4 ÷ (48 × 0.80 × 0.95 × 0.95) × 1.25 = 433 Ah.
- That is 20.8 kWh nominal, or 5 modules of 100 Ah; load current 62.5 A.
Result:
| Required capacity (Ah) | 433 |
|---|---|
| Nominal energy (kWh) | 20.8 |
| Battery modules needed | 5 |
| Load current (A) | 62.5 |
| Discharge rate (C-rate) | 0.144 |
Frequently asked questions
What DoD should I use?
Lead-acid VRLA batteries are often designed for 50–80% DoD for acceptable life; lithium (LFP) can use 80–90%. Follow the manufacturer’s cycle-life curve.
Why an ageing margin?
Batteries lose capacity over life; sizing for end of life (typically 80% of rated capacity) avoids early shortfalls.
Sources and further reading
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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.