The 603B is a handheld battery capacity analyzer designed to test 6 and 12 volt sealed lead acid batteries with capacities up to 100 ampere hour (Ah). It measures open and loaded battery voltage, state of charge (SOC), and internal resistance (IR) within seconds of connection, with measurement accuracy of 0.2% ±10 mV for voltage, 0.2% ±10 mA for current, and 5% ±1 mO for resistance. The analyzer features a built-in USB port, internal memory to store up to 50 battery records with test configurations and measurement results, a real-time clock for date and time stamping, and a programmable DC electronic load capable of 0.5 to 10 amperes for 0.5 to 5 seconds. Additional capabilities include charger circuit testing for 6, 12, or 24 volt systems, user-configurable pass/fail criteria based on nominal internal resistance, and computer software for pre-configuration and data export to CSV format. The 603B is ideal for maintenance programs in intrusion detection, fire alarm, security camera, access control, and industrial control systems where periodic battery testing and record keeping are essential.