[Clem1640]

A battery beak can be used to diagnose two battery problems:

First, It provides an internal resistance (derived from the voltage at 1 and 18 amps). The lower the better and internal resistance generally charts the health of the battery. The "Good", "Fair" & "Bad" ratings are determined by internal resistance only. This, therefore, provides a ranking method. Beware, though, because there tends to be some noise in this signal.

Second, the voltage at 0 amp (and % charged) will let you know if your battery loses a cell. A fully charged battery should read >100% charged on the battery beak. If you're down around 90% or lower and your charger indicated a full charge, you are down a cell.