Ah vs Wh: Why Battery Buyers Misread the Specs

A persistent confusion in battery shopping came back into focus this week as energy-storage searches climb to record levels in 2026. The two units at the center of the debate — amp-hours (Ah) and watt-hours (Wh) — are not interchangeable, yet most retail listings still pitch Ah as if it alone decides runtime.

Ah measures electric charge: the amount of current a battery can deliver over time. A 100Ah pack can theoretically push 100 amps for one hour, or 10 amps for 10 hours. But Ah is voltage-blind. It says nothing about how much actual work the battery can do, because voltage is left out of the equation.

Wh closes that gap. The formula is simple — Wh = Ah × V — but the consequence is large. A 12V 100Ah battery stores 1,200Wh. A 24V 100Ah battery stores 2,400Wh. Same Ah number, double the energy. For buyers comparing a 48V 30Ah pack against a 60V 25Ah pack, the first holds 1,440Wh and the second 1,500Wh; the smaller Ah figure wins on real capacity.

Ah still matters for wiring. Fuse ratings, cable gauge and C-rate calculations all run on current, not energy. But for runtime, appliance matching and price-per-stored-kWh, Wh is the unit that counts.

The practical rule: never compare batteries by Ah across different voltages. Convert to Wh first. And remember usable energy is lower than rated Wh — lead-acid gives about 50% depth-of-discharge, lithium 80–90%. The spec sheet is only half the story; the watt-hour line is the one to circle.