BATTERY POWER LAB · TRANSPARENCY

Our Calculation Methodology

An estimate is only as useful as the assumptions you can see.

Start with units

Internally, we use watts, watt-hours, amperes, amp-hours, volts and hours. Unit conversions happen at the input boundary. We calculate with unrounded values and round only the displayed answer, normally to two decimal places.

Keep the losses on the right side

For an AC load, battery draw is AC watts divided by inverter efficiency, plus battery-side idle draw. We apply usable capacity once. Direct DC mode assumes the entered watts are already the battery-side load and does not apply inverter losses.

Define reserve explicitly

Additional planning reserve multiplies the energy need by 1 plus the reserve fraction. It is not a remaining state-of-charge percentage. Usable capacity is a separate input. Defaults are editable illustrations, not manufacturer recommendations.

Separate energy from output power

Appliance energy includes usage duration and duty cycle. Running-output requirements use the sum of running watts, even for cycling loads. Startup totals assume simultaneous starts. A blank startup value stays unknown; we also show the known lower bound.

Charging and solar are scenarios

Charging uses constant battery-side output and an explicit storage-efficiency assumption. It does not model taper. Solar uses rated array watts, equivalent peak sun hours and one net performance factor. It does not model local weather or detailed PV behavior.

Product comparison is a screening step

Products can be excluded for insufficient capacity, running output, verified startup limits or regional mismatch. A product that passes those checks still requires verification of unknown surge, frequency, exact outlets, startup duration and appliance constraints. No tool declares a product universally compatible.

Validation and corrections

Our automated tests cover independently reasoned reference examples, invalid inputs, inverse conversions, monotonic relationships and equipment rounding. Automated tests are not engineering certification. We publish relevant primary sources and provide correction guidance.

Scope boundaries

These tools cover consumer estimates and ordinary plug-in loads. They exclude installation-grade wiring, protection and three-phase design, roof engineering, medical life-support systems, whole-home integration, transfer switches and battery/BMS compatibility.