SpecCalc Hub · Planning estimate
Battery Runtime Calculator
Estimate usable Wh and backup hours from Ah or Wh, voltage, battery count, depth of discharge, efficiency and load.
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8 h 38 min
Formula
nominal_wh = capacity converted to Wh * battery_count usable_wh = nominal_wh * DoD * efficiency runtime_hours = usable_wh / load_w
Assumptions
- Inputs are user-provided.
- Results are preliminary estimates.
- Load is constant and battery capacity is accurate.
Limitations
- Does not model age, temperature, порог отключения BMS, voltage sag, surge loads, or Peukert effect.
Sources / methodology
Converts battery capacity to usable Wh and divides by load.
- Formula version
- 1.0.6
- Formula review date
- 2026-05-25
Source links
Quick answer: This battery runtime calculator estimates backup hours after converting Ah or Wh capacity into usable energy. It keeps voltage, battery count, depth of discharge, efficiency and load visible so 12 V, 24 V and 48 V runtime estimates stay transparent.
Input parameters
- Capacity of one battery: 100
- Capacity unit: Ah
- Voltage of one battery (V): 12 V
- Battery count (pcs): 1 pcs
- Depth of discharge (%): 80 %
- System efficiency (%): 90 %
- Load (W): 100 W
Output values
- Nominal energy (Wh)
- Usable energy (Wh)
- Runtime (h)
- Runtime (min)
Step-by-step example
Calculation for the example inputs shown above:
- E₀ = 100 × 12 × 1 = 1,200 Wh
- E = 1,200 × 80% × 90% = 864 Wh
- t = 864 ÷ 100 = 8.64 h ≈ 8 h 38 min
Enter capacity and voltage of ONE battery. For an already combined bank enter its total parameters and set count to 1. This is not a wiring diagram.
How long will a battery last?
Battery runtime depends on usable energy, not only the label capacity. After converting Wh or Ah into usable Wh, divide by the load power to estimate hours, then keep battery age, temperature and cutoff behavior as separate limitations.
Battery runtime calculator in Wh and Ah
If the label is already in Wh, the page can work directly from that value. If the label is in Ah, voltage is still required because Ah alone is not energy; the calculator first converts Ah x V into Wh.
Battery runtime formula
The simplified method is nominal_Wh = capacity converted to Wh x battery_count, usable_Wh = nominal_Wh x depth_of_discharge x efficiency, and runtime_hours = usable_Wh / load_W. This keeps the estimate transparent instead of hiding the main assumptions.
Worked example: 12 V 100 Ah battery
A 12 V 100 Ah battery has 1200 Wh of nominal energy. If depth of discharge is 80% and system efficiency is 90%, the usable energy is about 864 Wh. A 200 W load would therefore run for about 4.3 hours in the simplified model.
Comparing 12 V, 24 V and 48 V battery setups
Voltage does not create extra energy by itself, but it changes how Ah translates into Wh. That is why battery systems should be compared in usable Wh first and only then in runtime hours.
| Battery setup | Nominal energy | Usable energy at 80% DoD and 90% efficiency | Runtime at 200 W |
|---|---|---|---|
| 12 V x 100 Ah | 1200 Wh | 864 Wh | 4.3 h |
| 24 V x 100 Ah | 2400 Wh | 1728 Wh | 8.6 h |
| 48 V x 50 Ah | 2400 Wh | 1728 Wh | 8.6 h |
Why manufacturer runtime can still differ
Real batteries and UPS packs do not always deliver nameplate energy at every discharge rate. Age, temperature, voltage sag, BMS cutoff, inverter conversion loss and manufacturer test conditions can all move the real runtime away from the simplified estimate.
Battery runtime vs UPS runtime
Use the general battery runtime page when you know battery capacity and load. Use the UPS Runtime Calculator when VA, power factor, UPS limits and manufacturer runtime behavior matter.
Worked examples
Worked example with the form defaults
Example inputs: Capacity of one battery: 100; Capacity unit: Ah; Voltage of one battery: 12 V; Battery count: 1 pcs; Depth of discharge: 80 %; System efficiency: 90 %; Load: 100 W. E₀ = 100 × 12 × 1 = 1,200 Wh. E = 1,200 × 80% × 90% = 864 Wh. t = 864 ÷ 100 = 8.64 h ≈ 8 h 38 min. Enter capacity and voltage of ONE battery. For an already combined bank enter its total parameters and set count to 1. This is not a wiring diagram.
Alternative calculation scenario
Example inputs: Capacity of one battery: 100; Capacity unit: Ah; Voltage of one battery: 12 V; Battery count: 1 pcs; Depth of discharge: 80 %; System efficiency: 90 %; Load: 200 W. E₀ = 100 × 12 × 1 = 1,200 Wh. E = 1,200 × 80% × 90% = 864 Wh. t = 864 ÷ 200 = 4.32 h ≈ 4 h 19 min. Enter capacity and voltage of ONE battery. For an already combined bank enter its total parameters and set count to 1. This is not a wiring diagram.
What the result does not establish
When you enter capacity for a complete battery bank, set the count to one. Constant-voltage energy arithmetic does not reproduce lead-acid rate effects, battery ageing or a BMS shutdown curve.
Common mistakes
- Keep all units consistent with the field labels.
- Check whether the input values are measured, nameplate values or planning assumptions.
- Review the stated assumptions and limitations before using the estimate.
What to check next
Check the inputs, limitations, sources and related calculators before using the estimate in a real decision.
FAQ
How long will a 12 V 100 Ah battery run a 200 W load?
A simplified estimate gives about 4.3 hours if you assume 80% depth of discharge and 90% system efficiency. Without those reductions, the nameplate energy would look higher than the usable energy.
Why do I need voltage when capacity is in Ah?
Because Ah alone is not energy. Voltage is needed to convert Ah into Wh so different battery systems can be compared on the same energy basis.
Should I include depth of discharge and efficiency?
Yes. Depth of discharge reduces usable capacity, and efficiency accounts for losses in the battery and the surrounding DC or inverter system.
Does higher system voltage automatically mean longer runtime?
Not by itself. Higher voltage changes how Ah converts to Wh, but runtime still depends on total usable energy and the actual load.
Can Ah alone compare two different battery banks?
No. Ah must be combined with voltage so both systems are compared on the same Wh basis before you compare runtime.
Can this replace manufacturer runtime data?
No. The page is a transparent planning estimate and does not replace manufacturer curves, battery aging data, cutoff behavior or application-specific testing.
Related calculators
Battery capacity, load and real runtime
Estimate battery runtime from voltage, amp-hours, discharge depth, efficiency and load. Separate nominal energy from the energy actually available.
Energy to runtime
Nominal Wh = V × Ah; usable Wh = nominal Wh × DoD × efficiency; hours = usable Wh / load W. Use fractions for DoD and efficiency. A whole-pack Ah rating must not be multiplied by battery count a second time.
12 V, 9 Ah battery with a 24 W load
A 12 V, 9 Ah battery stores nominally 108 Wh. With an illustrative 80% usable discharge and 90% efficiency, usable energy is 77.76 Wh. A constant 12 V, 2 A load is 24 W, so 77.76 / 24 = 3.24 h, about 3 h 14 min. Actual time depends on chemistry, age, temperature and cutoff.
What the estimate cannot establish
A BLDC motor nameplate power is not its average electrical draw throughout a ride. Use measured input energy or a representative average load; starting current, BMS limits and voltage sag remain separate constraints.
Can two batteries with the same Ah run for different times?
Yes. Different voltage means different Wh; usable discharge, efficiency, condition and load also change runtime. Compare usable energy, not Ah alone.
Should I enter one battery or the whole bank?
Use the capacity and voltage of one battery with its count. If entering an already combined bank energy, set count to one to avoid counting that energy again.
Why can real runtime be shorter than this result?
The estimate uses the entered usable fraction and efficiency. Battery ageing, temperature, high discharge current, inverter self-consumption and low-voltage cutoff may reduce available runtime further.
Continue the calculation
This calculator provides an estimate for informational purposes only. It is not a certified engineering design, electrical safety approval, or professional installation recommendation. Always verify final decisions with a qualified professional and applicable local codes.