I had just gotten the m18 XC 3.0 packs with my new M18 set, they last along time but i drill 40 to 50 1 1/2 holes through 3" beams every day, so I use the 4.0 packs and they last me around 30 or so holes. and a good way to find cheap packs would be ebay or amazon. Ive found a listing of 4 4.0 packs on ebay for $200.