Battery Runtime Calculator: method, checked example and practical limits
Estimate usable energy and runtime from battery voltage, capacity, load and efficiency. The hours are an energy-budget estimate rather than a battery discharge test under the actual load.
Inputs used by this calculator
Battery Runtime Calculator uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Battery voltage (V) | 12 | 0.000001 to 1000000 | Supplies the battery voltage (v) quantity used by the published equation or result breakdown. |
| Battery capacity (Ah) | 100 | 0.000001 to 1000000000 | Supplies the battery capacity (ah) quantity used by the published equation or result breakdown. |
| Average load (W) | 300 | 0.000001 to 1000000000000 | Supplies the average load (w) quantity used by the published equation or result breakdown. |
| System efficiency (%) | 90 | 0.01 to 100 | Supplies the system efficiency (%) quantity used by the published equation or result breakdown. |
| Usable depth of discharge (%) | 80 | 0.01 to 100 | Supplies the usable depth of discharge (%) quantity used by the published equation or result breakdown. |
Inputs and measurement conventions
The quantities used on this page are Battery voltage (V), Battery capacity (Ah), Average load (W), System efficiency (%), Usable depth of discharge (%). Start with values for the same situation and read the units attached to each field. The field reference below shows supported choices and numerical limits.
Amp-hours alone cannot compare batteries at different voltage. Inverter idle draw, temperature and aging affect delivered energy.
Method and equation
Multiply nominal voltage and amp-hours for stored watt-hours, apply efficiency and usable fraction, then divide by load watts.
Battery Runtime Calculator uses the following stated relationship: runtime hours = voltage × amp-hours × efficiency × usable fraction ÷ watts. Its assumptions determine which question the answer can resolve.
runtime hours = voltage × amp-hours × efficiency × usable fraction ÷ wattsWorked calculation with the starting values
Battery voltage (V): 12; Battery capacity (Ah): 100; Average load (W): 300; System efficiency (%): 90; Usable depth of discharge (%): 80. These starting values give 2.88 estimated runtime hours. The calculation breakdown is Nominal energy (Wh): 1,200; Usable energy (Wh): 864; Runtime minutes: 172.8; Average load: 300.
12 V × 100 Ah at 90% efficiency and 80% usable capacity provides 864 Wh, or 2.88 hours at 300 W.
Reading the answer
The hours are an energy-budget estimate rather than a battery discharge test under the actual load.
Nominal energy (Wh): 1,200; Usable energy (Wh): 864; Runtime minutes: 172.8; Average load: 300. These intermediate quantities make the stated Battery Runtime Calculator model inspectable; they should be read together with the main answer rather than treated as independent guarantees.
Common errors and model boundaries
Amp-hours alone cannot compare batteries at different voltage. Inverter idle draw, temperature and aging affect delivered energy.
Temperature, aging, discharge rate, inverter idle draw and battery management limits change real runtime.
Independent verification and next decision
The model predicts that relationship, but real capacity and conversion efficiency may change with discharge rate.
For the Battery Runtime Calculator method, compare runtime hours = voltage × amp-hours × efficiency × usable fraction ÷ watts with the starting inputs and the calculation table. The linked U.S. Department of Energy: energy storage and NIST Guide to the SI and National Institute of Standards and Technology references identify the relevant definitions, conventions or domain limitations. Retain intermediate precision when comparing a manually worked answer.
Battery Runtime Calculator worked-example ledger
| Quantity | Example value | Role |
|---|---|---|
| Battery voltage (V) | 12 | Entered assumption |
| Battery capacity (Ah) | 100 | Entered assumption |
| Average load (W) | 300 | Entered assumption |
| System efficiency (%) | 90 | Entered assumption |
| Usable depth of discharge (%) | 80 | Entered assumption |
| Main answer | 2.88 estimated runtime hours | Calculated from the starting inputs |
| Nominal energy (Wh) | 1,200 | Intermediate or contextual output |
| Usable energy (Wh) | 864 | Intermediate or contextual output |
| Runtime minutes | 172.8 | Intermediate or contextual output |
| Average load | 300 | Intermediate or contextual output |
Frequently asked questions
Does doubling load always halve actual runtime?
The model predicts that relationship, but real capacity and conversion efficiency may change with discharge rate.
Which relationship does the Battery Runtime Calculator use?
Multiply nominal voltage and amp-hours for stored watt-hours, apply efficiency and usable fraction, then divide by load watts. The displayed relationship is runtime hours = voltage × amp-hours × efficiency × usable fraction ÷ watts.
What do the starting values produce in the Battery Runtime Calculator?
Battery voltage (V): 12; Battery capacity (Ah): 100; Average load (W): 300; System efficiency (%): 90; Usable depth of discharge (%): 80. These starting values give 2.88 estimated runtime hours. The calculation breakdown is Nominal energy (Wh): 1,200; Usable energy (Wh): 864; Runtime minutes: 172.8; Average load: 300.
How should I interpret this Battery Runtime Calculator answer?
The hours are an energy-budget estimate rather than a battery discharge test under the actual load.
Which input mistake most affects the Battery Runtime Calculator?
Amp-hours alone cannot compare batteries at different voltage. Inverter idle draw, temperature and aging affect delivered energy.
What is outside this Battery Runtime Calculator model?
Temperature, aging, discharge rate, inverter idle draw and battery management limits change real runtime.
What to keep in mind
Temperature, aging, discharge rate, inverter idle draw and battery management limits change real runtime.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.