Practical guide

Measuring Electrical Load for a Runtime Estimate

Choose a useful watts or amps measurement interval, distinguish AC and DC paths, and capture cycling or standby loads for battery runtime planning.

Decide which side of the system you are measuring

An AC appliance measurement gives output-side power. A battery-side DC measurement can already include inverter loss and idle draw. Do not apply the same loss twice. Mark every reading with its location, voltage, units, instrument and operating state.

Use a representative interval

A cycling device can look very different at startup, while active, and asleep. Capture the states and the fraction of time in each, or use a sufficiently long energy reading to calculate an average. Record surge separately because average watts cannot approve surge capability.

Convert current only with voltage

For a DC load, watts are volts times amps at the measured point. Current alone is not an energy input. For AC systems with power factor or nontrivial waveforms, use suitable equipment and professional guidance rather than assuming simple DC arithmetic.

Preserve uncertainty honestly

Write down measurement resolution, variation, and whether a nameplate or live measurement was used. Do not hide uncertainty by entering more digits than the source supports.

Use the collected values in the battery runtime calculator, which keeps direct DC and inverter paths separate.