UPG 6-Volt 4.5 Ah Sealed Lead Acid (SLA) AGM Rechargeable Battery UB645 - The Home Depot
Mighty Max Battery ML7-6 6V 7AH SLA Battery F1 Terminal- PACK OF 4 Rechargeable Sealed Lead Acid 670 Backup Power Batteries (4-Pack) in the Device Replacement Batteries department at Lowes.com