Mighty Max Battery ML4-6- 6V 4.5AH for YT-645 with F1 Terminal Rechargeable Sealed Lead Acid 645 Backup Power Batteries in the Device Replacement Batteries department at Lowes.com
YT-645 Yuntong replacement SLA Battery (6V 4.5AH)
6V 4.5AH SLA Replacement Battery for Yuntong YT-645-3 Pack