BTL21 is an intelligent test probe designed for use with Fluke 500 Series Battery Analyzers, featuring an integrated LCD display and infrared temperature measurement capability. The probe enables automatic measurement storage of voltage, resistance, and temperature readings during sequence testing of battery strings, eliminating the need to manually save each measurement. It incorporates rugged coaxial two-pole Kelvin test pins with a remote SAVE button to reduce test time and increase efficiency, along with verbal audio feedback to confirm measurements. The BTL21 is ideal for maintenance, troubleshooting, and performance testing of stationary batteries and battery banks in critical backup applications, providing enhanced data accuracy and streamlined workflow for battery diagnostics.