APC Smart-UPS Ultra SRTL50RMBP1U-LI - External Lithium-Ion Battery Module, 18.85 Ah, 1U The APC Smart-UPS Ultra SRTL50RMBP1U-LI is a high-performance external lithium-ion battery module designed to extend the runtime of compatible APC Smart-UPS Ultra UPS systems. With a battery capacity of 18.85 Ah and a voltage of 50.4 V, it provides additional power reserves during power outages. Thanks to its compact height of just 1U, the battery module is particularly well-suited for space-saving use in server racks and IT infrastructures. Modern lithium-ion technology enables low-maintenance operation with a long service life.