Power Sonic - PS-640F1, 6 Volt, 4.5 AH Rechargeable SLA Battery
Universal Power Group 6V 5Ah Spring Top AGM Battery, 45954 at Tractor Supply Co.
Duracell 6 Volt Battery (5AH) - Toy Store Discount
UPG General Purpose Deep Cycle AGM Rechargeable Sealed Lead Acid 650 Backup Power Batteries in the Device Replacement Batteries department at Lowes.com
6 Volt 5aH Rechargeable Battery, Lantern Style - Parts & Accessories - Feeders