UPG General Purpose Deep Cycle AGM Rechargeable Sealed Lead Acid 645 Alarm System Batteries in the Device Replacement Batteries department at Lowes.com
6 Volt 4AH Rechargeable Sealed Lead Acid SLA Battery 6 volt 4amp - Walmart.com
NPP Power NP6-4Ah 6V 4.5Ah Replacement Battery (2 Pack)