Home Depot is selling a single 6Ah battery for $129, this is 2 batteries for $59.50 each. Free S/H. Online only AFAICT.
https://www.homedepot.c
Also 2-pack of 9Ah batteries for $179 ($89.50 each):
https://www.homedepot.c
And 4-pack of 9Ah batteries for $349 ($87.50 each):
https://www.homedepot.c