just got a 765CFM blower with the free 2.5Ah battery... is there a cheap way to buy a 5Ah battery?

just got a 765CFM blower with the free 2.5Ah battery at Lowe's. (in addition to the included 5Ah battery)

is there a cheap way to buy a 5Ah battery? or is the only way to wait for a sale on a tool that I may need in the future?

Thanks!