Yuntong YT-645 6V 4.5Ah Sealed Lead Acid Replacement Battery: BatteryClerk.com
6V 4.5AH Replacement Battery for Yuntong YT-645 82481354100 | eBay
YT-645 6 Volt 4.5 Ah SLA Replacement Battery w/ F1 Terminal
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