The top chart compares rated, usable, and remaining energy. The bottom chart shows a cycle-life curve with your chosen discharge point.
Typical limits vary by chemistry and manufacturer. Use these as planning references.
| Battery type | Typical recommended DoD | Cycle estimate at 80% DoD | Notes |
|---|---|---|---|
| LiFePO₄ | 90% | ~3,500 | Strong cycle life; keep reserve for outages. |
| NMC / NCA | 80% | ~2,000 | Higher energy density; watch temperature. |
| LTO | 95% | ~7,000 | Excellent power and cycle life; higher cost. |
| Lead-Acid (AGM) | 50% | ~700 | Deeper discharge shortens life quickly. |
| Lead-Acid (Flooded) | 50% | ~600 | Needs maintenance; sensitive to high current. |
| NiMH | 70% | ~1,000 | Moderate performance; less common for large banks. |
Rated Energy (Wh): Wh = Ah × V (or use entered kWh × 1000).
Applied DoD (%): min(DoD limit, 100 − Reserve SoC).
Total Derate: BatteryEff × InverterEff × TempFactor × AgingFactor × PeukertFactor.
Usable Energy from Full (Wh): RatedWh × (AppliedDoD/100) × TotalDerate.
Remaining Usable Energy (Wh): RatedWh × ((SoC Now − Reserve SoC)/100) × TotalDerate.
Runtime (hours): RemainingWh ÷ LoadW (when LoadW > 0).
- Select the capacity mode: enter Ah and voltage, or enter kWh directly.
- Choose your battery chemistry so the calculator can apply typical limits.
- Set your current state of charge and the reserve you want to keep.
- Add efficiency, temperature, and aging factors for realistic usable energy.
- Enter a load power to estimate remaining runtime at that load.
- Press Calculate, then download CSV or PDF if needed.
Why depth of discharge matters
Depth of discharge (DoD) is the percent removed from a full battery. A 10.0 kWh bank at 80% DoD makes 8.0 kWh accessible before reserve or losses. Pushing DoD higher can raise short‑term runtime, but it usually accelerates wear. Tracking DoD also helps compare banks sized in Ah×V versus kWh, because energy is the true driver of runtime. Many installers target daily DoD below 70% for resilience in practice.
Applying chemistry limits and reserve
Chemistry sets practical DoD limits. Typical planning values are about 90% for LiFePO₄, 80% for NMC, and 50% for lead‑acid. Reserve SoC can tighten the limit further. If you keep a 20% reserve, the maximum discharge from full is 80%, even when the chemistry supports more. The calculator applies the lower of the DoD limit and (100 − reserve).
Efficiency, temperature, and aging derates
Delivered energy is reduced by losses and derating. Example: 8.0 kWh usable from full, battery efficiency 96%, inverter efficiency 92%, temperature factor 85%, and aging factor 90% gives a total multiplier of 0.96×0.92×0.85×0.90 = 0.676. The energy available to loads becomes 8.0×0.676 = 5.41 kWh. These adjustments prevent optimistic runtime estimates.
Runtime and sizing using load targets
Runtime is remaining usable energy divided by load power. If remaining energy is 1.80 kWh and the load is 500 W, expected runtime is 1.80/0.50 = 3.60 hours. For sizing, energy demand equals load×time. A 500 W load for 4 hours needs 2.0 kWh. With an applied DoD of 80% and total multiplier of 0.88, minimum rated energy is 2.0/(0.80×0.88) = 2.84 kWh.
Cycle-life tradeoffs and cost impact
Lower DoD typically extends cycle life. If a chemistry delivers about 3,500 cycles near 80% DoD, stepping down to 60% can increase the estimate by roughly (80/60)^1.25 ≈ 1.5×, or about 5,200 cycles. The tradeoff is more installed capacity for the same usable energy. The chart helps visualize rated energy versus usable and remaining energy so you can balance performance and longevity.
What is depth of discharge?
Depth of discharge is the percentage of a battery’s full capacity that has been used. If SoC is 65%, the DoD from full is 35%. Higher DoD generally increases wear, especially for lead-acid.
How is the applied DoD limit chosen?
The calculator takes the lower of your DoD limit and the reserve constraint. Reserve sets a maximum discharge of (100 − reserve SoC). This prevents calculations that violate your minimum kept charge.
Why do efficiency settings matter?
Battery and inverter losses reduce energy delivered to loads. A 96% battery efficiency and 92% inverter efficiency deliver about 0.883 of the stored energy. Using realistic values avoids overstated runtime.
When should I use the lead-acid adjustment?
Use it when your chemistry is lead-acid and you know discharge current. Higher current reduces effective capacity. The adjustment is optional, but it improves planning for large loads and small banks.
Does the cycle-life estimate guarantee performance?
No. It is a planning estimate based on a simple curve and a typical cycle baseline. Real cycle life depends on temperature, charge rates, cell quality, voltage limits, and calendar aging.
How do I size for a target runtime?
Multiply load power by target hours to get energy needed. Then divide by (applied DoD × total derate). The result is the minimum rated energy capacity to meet that runtime under your assumptions.