What is the difference between Ah and Wh?

Ah (amp-hours) is charge capacity — current × time. Wh (watt-hours) is energy — voltage × Ah. They are related by voltage: Wh = V × Ah. The same Ah means very different energy at different voltages, which is why Wh is the honest comparison across chemistries.

How do I convert Ah to Wh?

Multiply amp-hours by the nominal voltage: Wh = V × Ah. A 100 Ah 12V lead-acid battery is ~1,200 Wh; a 100 Ah 3.2V LFP cell is only ~320 Wh. That is why comparing two batteries by Ah alone can be misleading.

Technology · Units · Last reviewed 2026-09-14

Ah vs Wh: The Difference Between Amp-Hours and Watt-Hours

Amp-hours and watt-hours are both "capacity" numbers, but they measure different things — and confusing them is how two batteries with the same Ah end up storing very different amounts of energy.

Direct answer: Ah (amp-hours) is charge capacity — how many amps for how long (current × time). Wh (watt-hours) is energy — the actual work stored (voltage × Ah). They are related by voltage: Wh = V × Ah. Because voltage differs between chemistries, the same Ah means different energy — a 100 Ah 12V battery holds ~1,200 Wh, while a 100 Ah 3.2V LFP cell holds only ~320 Wh.

The two units

	Ah (amp-hours)	Wh (watt-hours)
Measures	Charge capacity	Energy
Formula	current × time	voltage × Ah
Independent of voltage?	No — charge only	Yes — the true energy

Ah tells you how much charge the battery holds; Wh tells you how much energy. The voltage is the missing piece that connects them.

Why the voltage matters

Two batteries with identical Ah but different voltages store different energy. A 100 Ah lead-acid battery at 12V stores about 1,200 Wh. A 100 Ah LFP cell at 3.2V stores about 320 Wh — less than a third. This is why Wh is the honest unit for cross-chemistry comparison: it already accounts for voltage, while Ah does not.

When to use each

Same voltage, same chemistry — Ah is fine (e.g. comparing two 12V lead-acid batteries).
Different voltages or chemistries — convert to Wh, or the comparison is misleading.
Range and energy capacity — Wh is what matters (an EV pack's energy is quoted in kWh, which is 1,000 Wh).

Common misconceptions

"Ah is the energy." No — Ah is charge. Energy is Wh, which is Ah multiplied by voltage.
"Two batteries with the same Ah store the same energy." Only at the same voltage. A 100 Ah 12V and a 100 Ah 3.2V battery differ by ~3.75× in energy.
"Wh and Ah are interchangeable." They are not — you need the voltage to convert.

Key takeaways

Ah = charge (current × time); Wh = energy (voltage × Ah).
The relationship is Wh = V × Ah.
The same Ah means different energy at different voltages — compare in Wh across chemistries.
EV packs are quoted in kWh (1,000 Wh), which is the energy figure.

The Author's Take

Position: The Ah-vs-Wh confusion is the single most common unit error in battery buying — and it quietly rewards the seller who quotes a big Ah number while hiding a low voltage.

Reasoning: Ah looks like energy but is only charge, so a battery can be quoted with a flattering Ah while storing modest energy. The fix is one multiplication: convert everything to Wh and the comparison becomes honest. Anyone comparing batteries across chemistries should default to Wh — and treat an Ah-only comparison as incomplete.

This is the author's editorial view, not a purchasing guarantee.

Sources

Cross-verified from battery engineering references. The Ah/Wh relationship is a standard unit conversion (Wh = V × Ah).

Battery engineering references — charge and energy unit definitions.
Manufacturer datasheets — nominal voltage and capacity specifications.

Last reviewed: 2026-09-14