1. A method of predicting the available energy of a battery comprising the steps of: determining the battery internal resistance (IR); measuring the battery open circuit voltage (OCV) and temperature (T); calculating the voltage and current points (V gas and I gas ) at which the battery transitions from one of a charge to overcharge or overcharge to charge state in response to at least one of battery charge and discharge; and predicting the available energy on the basis of the parameters OCV, T, IR, V gas and I gas.