Milliamp-hours measure charge. Watt-hours measure energy. For cells of the same voltage they rank the same way, so mAh is a fair shorthand — which is why Ni-MH cells are sold on it. The moment two cells run at different voltages, mAh stops comparing anything useful.

Multiply capacity by voltage and you get energy. Our AA Ni-MH at 1000mAh × 1.2V is about 1.2Wh. Our AA Type-C lithium is rated 4255mWh, which is 4.26Wh. That is the honest comparison, and it is why the lithium cell is listed on energy rather than on charge.

One caveat: energy in the cell is not runtime in your device. A regulated 1.5V cell spends some of that energy in its own converter, and your device's cut-off voltage decides how much of the rest it can actually use. Test in the product before you write a runtime claim on the packaging.

Use this checklist

  • mAh compares fairly only at the same voltage
  • Energy in Wh = capacity in Ah × nominal voltage
  • Regulated cells lose some energy in conversion
  • Runtime is a device measurement, not a cell measurement