Home Depot offers the Ridgid 12-Volt 4.0Ah Hyper Lithium-Ion Battery 2-Pack, model no. AC820592, for $34.50 with free shipping. That's $6 under our July mention and the lowest total price we've seen. (It's a current low by $25.) They're compatible with all Ridgid 12V tools and chargers. Deal ends August 30.