Electrical calculators
Works in your browser. Nothing is uploaded.Battery runtime
Work out how long a battery runs a load, from its capacity, its voltage and how much of it you can use.
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A load in amps is taken at the battery’s voltage. With an inverter, the battery also covers what the inverter loses.
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%
Runtime
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Usable energy
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From the battery
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Electrical calculators
Resistor color codeBands to ohms and back.Ohm’s law and powerVolts, amps, ohms and wattsVoltage drop and cable sizeThe drop over a run, and the smallest cable within itWire sizesAWG, mm², kcmil and diameterLED resistorThe resistor an LED needsSMD codesResistor and capacitor markings555 timerAstable and monostableBattery runtimeHow long a battery lasts
How to use it
- Describe the battery
Its capacity in Ah or Wh, its voltage and how much of the charge you can use.
- Add the load
In watts, or in amps at the battery’s voltage, and whether it runs through an inverter.
- Read the runtime
Hours and minutes, the usable energy and the current drawn from the battery.
Tips
- Usable charge
Lithium batteries give about 80 to 90 % of their capacity. Lead-acid lasts longer kept to about 50 %.
- No inverter
Lights, pumps and fridges that run straight off the battery skip the inverter’s loss.
- Allow some spare
Batteries give less in the cold and at high currents, and less as they age.
In the app
Electrical calculator in Angle Meter
- Solar strings for the coldest day
- Power station and generator sizing
- Energy use a day, a month and a year
- Power strip load checks
Get it onGoogle PlayComing soon to the App Store
Electrical calculator guide ›