Charge units — coulomb, mAh and ampere-hour
Charge (C or Ah) is not energy (Wh). Multiply Ah by voltage to get Wh. Ignore voltage and lithium and lead-acid look interchangeable — they are not.
Charge and energy are related but distinct. Charge is quantity of electrons; energy is charge times voltage. Battery specs frequently muddle them, and equivalent-sized packs from different chemistries deliver wildly different runtimes.
The exact factors
1 A·h = 3600 C > 1 mA·h = 3.6 C > Energy (W·h) = charge (A·h) × voltage (V)
Where each is used
Coulomb: electrochemistry, capacitor sizing, semiconductor doping. mAh, Ah: batteries, small-signal current integration, plating time. C-rate: discharge/charge current expressed as multiples of Ah capacity (a 3 Ah pack at 2C draws 6 A).
Worked example — power bank comparison
Two power banks: 20 000 mAh at 3.7 V vs 6000 mAh at 12 V. Charge: 20 vs 6 Ah. Energy: 74 vs 72 Wh — essentially identical. Buyers who compare mAh alone miss the voltage rescaling.
Recap
Ah is charge. Wh is energy. Multiply by voltage to compare.
Try the converters mentioned in this article
FAQ
Is 1 F (farad) related to 1 C?+
Yes — 1 F = 1 C/V. A 1 F cap charged to 1 V stores 1 C of charge.
What is coulombic efficiency?+
Charge out ÷ charge in per cycle. Lithium is 99.9%+, lead-acid 85–90%.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.