Conversions

Battery Weight Comparison Calculator (Wh/kg)

Compare two batteries by specific energy (Wh/kg), usable energy per kilogram and the weight each needs to deliver the same usable energy.

Results are mathematical estimates from the values you enter — not measurements and not data about a specific product or vehicle.

A — nominal voltage

A — capacity

A — weight

A — usable DoD

B — nominal voltage

B — capacity

B — weight

B — usable DoD

Target usable energy (optional) (optional)

How does the Battery Weight Comparison Calculator (Wh/kg) work?

Specific energy = nominal voltage × capacity ÷ weight (Wh/kg). Because usable depth of discharge differs between chemistries, compare usable Wh/kg = Wh/kg × DoD. The weight needed for a target usable energy is that energy ÷ usable Wh/kg. Take voltage, Ah and weight from each datasheet.

Formula

Wh/kg = V × Ah ÷ kg
usable Wh/kg = Wh/kg × DoD
weight(target) = Wh(target) ÷ usable Wh/kg

Worked example

A: 12 V 100 Ah 30 kg, DoD 50% → 40 Wh/kg, 20 usable Wh/kg. B: 12.8 V 100 Ah 12 kg, DoD 80% → 106.7 Wh/kg, 85.3 usable Wh/kg.

Limitations and warnings

The example values are illustrative inputs, not data of any specific product. Use datasheet weights (with or without terminals/handles as stated).
Weight alone does not decide suitability: starting current, charging system, temperature range and mounting matter.

Four values that are often confused

Nominal capacity (Ah): Charge a battery delivers under rated conditions, usually over 20 hours (C20) at 25 °C.
Usable capacity: The part of the nominal capacity you can use without damaging the battery — about 50% for lead-acid, 80–90% for LiFePO4.
Cranking current (CCA): Current deliverable for a short time in the cold to start an engine. It measures power, not stored charge, and cannot be converted to Ah.
Stored energy (Wh): Ah × voltage. The right unit to compare batteries of different voltages.