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.
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).
What do people get wrong about Ah and Wh?
- "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 conversion table
| System | Conversion | Example: 100 Ah |
|---|---|---|
| 12V | Ah × 12 | 1,200 Wh |
| 24V | Ah × 24 | 2,400 Wh |
| 48V | Ah × 48 | 4,800 Wh |
Same amp-hours, different energy — which is why Ah figures only compare within one voltage, and Wh is the honest cross-voltage unit.
Why This Matters
Where I stand: 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.
Why I think so: 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.
Frequently asked questions
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.
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