Battery energy systems for critical applications require monitoring techniques that properly inform equipment operators and maintenance personnel of battery integrity. While battery cells may appear as simple elements, a high voltage battery configuration has many complexities that must be monitored to ensure reliable performance. These include cell capacities, voltages, temperatures and interconnection resistances. Continuous data logging and evaluation of these parameters provide operating personnel with state of charge and alarm status for all relevant battery concerns. Long term data storage provides users and battery suppliers insight to battery performance under all conditions of use. Design and interfacing of data acquisition circuitry is critically important to ensuring reliable data measurements for assessment of the battery system.