Forecast battery life and replacement cost for active sites. Balance load, autonomy, and efficiency targets. Make replacement decisions with clear project outputs.
| Scenario | Load (kW) | Backup (h) | DoD (%) | Temp (°C) | Unit (V/Ah) | Unit Cost |
|---|---|---|---|---|---|---|
| Remote site office | 2.5 | 6 | 80 | 32 | 12 / 200 | 260 |
| Security lighting | 1.2 | 10 | 70 | 28 | 12 / 150 | 190 |
| Container workshop | 4.0 | 4 | 85 | 35 | 12 / 250 | 310 |
E_usable = Load_kW × Hours / InverterEffE_nom = E_usable / (DoD × RoundTripEff)E_unit(kWh) = V_unit × Ah_unit / 1000N_series = V_system / V_unitN_parallel = ceil(E_nom / (E_unit × N_series))Cycles_y = (Daily_kWh × 365) / BankUsable_kWhLife = min(Life_cycle, Life_calendar)Cost_future = Cost_today × (1+Inflation)^YearsRemainingPV = Cost_future / (1+Discount)^YearsRemainingField replacement planning often uses two limits: a calendar limit and a cycle limit. Lead-acid banks commonly target 3–6 years in hot construction zones, while lithium LFP banks frequently target 8–12 years with controlled charging. Typical lead-acid ratings cluster near 500–900 cycles at 80% DoD, whereas LFP can exceed 3,000–6,000 cycles. This calculator estimates both limits, then selects the shorter value to avoid optimistic schedules.
Usable energy is reduced by design depth of discharge and round-trip efficiency. For example, a 20 kWh nominal bank at 80% DoD and 90% round-trip efficiency yields about 14.4 kWh usable. Lowering DoD from 80% to 70% can improve life, but may require more units to meet the same backup duration.
Temperature is one of the strongest drivers of early replacement. Many sites above 35°C experience accelerated aging, especially for lead-acid. The calculator applies a conservative temperature factor that shortens life at higher temperatures and slightly extends life for cooler operation, with a cap to prevent unrealistic gains. Practical controls include shading enclosures, providing airflow, and avoiding prolonged full-charge storage in extreme heat.
The sizing section converts your critical load and backup hours into a required nominal energy, then recommends series and parallel counts based on system voltage and unit voltage. The result is a total unit count that aligns with common procurement line items and helps crews stage replacements without re-engineering the bank. Always verify that unit voltage divides system voltage evenly and that cable and breaker ratings match the string count.
Replacement cost combines material, labor, disposal, and logistics, then adds contingency and tax. The tool can also project a future replacement cost using inflation and report a present value using a discount rate. These outputs support lifecycle budgeting, tender comparisons, and scheduling replacements before capacity drops below your end-of-life threshold. Document commissioning tests to validate bank performance.
Nominal energy is the nameplate storage. Usable energy accounts for depth of discharge and efficiency losses, which determine how much energy actually supports your loads during backup.
Deeper cycles stress electrodes and increase heat and chemical wear. Many chemistries deliver more cycles when operated at a lower DoD, but you may need additional capacity to meet autonomy.
If you do not know daily usage, the calculator approximates daily energy from critical load and backup hours. For better accuracy, enter measured kWh/day from monitoring or energy logs.
Common planning thresholds are 80% for performance-sensitive sites and 70% for non-critical loads. Choose a value that matches your uptime expectations and the minimum autonomy you must maintain.
No. Both are affected, but lead-acid is typically more sensitive to sustained heat. Lithium can also degrade faster in heat, especially with high charge rates or high state-of-charge storage.
Yes. Use the override fields for cycle life and calendar life when you have datasheet values. This makes the replacement schedule and cost planning closer to your selected product line.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.