Lowes.com has Greenworks Pro 60-Volt Max 2Ah Rechargeable Lithium Ion Cordless Power Equipment Battery (LB60A00) for $64.50. Order online for in-store pickup (unavailable for shipping). Price only available at select locations.
I bought one as a secondary battery for my lawnmower and as a primary for my hand tools (the 5Ah can get heavy after a while on trimmers/saws).