Ah and Wh: Battery Capacity Explained

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Batteries are often labelled in amp-hours (Ah) — but what does this actually mean? And why is watt-hours (Wh) often a better measure? This guide explains both with practical examples.

Amp-hours (Ah) — Charge

Amp-hours (Ah) measure the amount of electrical charge in a battery. One amp-hour means the battery can supply 1 ampere for 1 hour.

• 100 Ah battery can supply: 1 A × 100 h = 100 Ah
• Same battery can supply: 10 A × 10 h = 100 Ah
• Or: 50 A × 2 h ≈ 100 Ah (approximately — Peukert effect)

Ah is useful when calculating charging time: charging time ≈ Ah needed / charger current (A).

Watt-hours (Wh) — Energy

Watt-hours (Wh) measure the actual energy content of a battery: Wh = Ah × Voltage (V). This is a more universal measure because it accounts for voltage.

Same Ah rating, but very different energy — that is why Wh is the better comparison unit.

EV Batteries

Electric vehicle batteries are always rated in kWh (kilowatt-hours) because this directly relates to driving range:

• Nissan Leaf 40 kWh → ~200 km range
• Tesla Model 3 Standard Range ~54 kWh → ~350 km
• Tesla Model 3 Long Range ~82 kWh → ~560 km