The most important battery state of health (SOH) parameter is capacity. Capacity, the energy storage capability of a battery, is difficult to measure for the valve regulated lead acid (VRLA) battery. One of the most reliable approaches involves fully discharging the battery. However, this leaves the telecommunication system vulnerable to mains failure, is expensive and time consuming. Recently the authors have discovered a correlation between battery capacity and parameters found within the voltage profile during the initial stages of discharge. This region is known as the coup de fouet. This paper presents the issues relating to the construction of a model for extracting battery capacity knowledge from the coup de fouet. Results obtained so far indicate that this approach will form the basis of an intelligent battery management system.