The Tadiran TL-5903 (also known as SL-360) is a 3.6 V lithium backup battery with a 2400 mAh capacity designed for industrial use. It is most commonly used as a replacement battery for the Siemens S7-400 PLC series (part number 6ES7971-0BA00) to provide long-term power for internal memory and real-time clock circuits when the main supply is off.

This battery uses lithium thionyl chloride (Li-SOCl₂) chemistry, which delivers very low self-discharge and long shelf life, making it ideal for retaining critical data in programmable logic controllers, automation systems, and other industrial electronics where reliability and long service life are essential.