Methodology

All calculators use one energy model. Inputs are editable; defaults are examples, not universal equipment specifications.

Battery energy

Use nominal battery voltage. For example, 100 Ah × 51.2 V = 5120 Wh. Charging voltage is a different quantity and is not used for this conversion.

Runtime and capacity

P is power in watts; E is energy in watt-hours; t is time in hours. η is conversion efficiency and f is the usable capacity fraction. In the formulas, 90% is written as 0.9. Idle consumption is added separately: use 0 W if it is already included in your efficiency figure.

Model limitations

• Load and efficiency are assumed to be constant averages.
• Usable capacity should account for starting charge, reserve and battery condition. From 90% to 20% charge means 70% of nominal energy for a new battery.
• Temperature, ageing, the Peukert effect in lead-acid batteries and voltage cutoffs are not modelled separately.
• Startup power, wiring, protection and equipment compatibility need separate assessment.

Sources & assumptions

Victron Energy: Lithium Smart Battery — System design and BMS selection

Victron Energy: SmartShunt battery monitoring

Methodology updated October 6, 2026