Interesting article from Battery University about measuring State of Charge (SoC) or remaining capacity for batteries or packs.

An excerpt:

Most users see the battery as an energy storage device resembling a fuel tank dispensing liquid fuel. For simplicity reasons, a battery can indeed be compared as such a vessel; however, measuring stored energy in an electrochemical device is far more complex than drawing fluid from a fixed container

Full article at http://batteryuniversity.com/learn/a...e_missing_link