Batch Sparging Efficiency

[BillyBock]

I'm new to all-grain brewing after 1 year of extract & grains. I decided to try batch sparging to keep my equipment list down to a min. For equipment I use: 5 gal Gott cooler (mash tun), bucket-in-bucket (lauter tun), and bottling bucket to collect 6-7 gals of wort. It's then boiled in two 20 qt SS pots. On batch #1 (an IPA), I achieved an extraction efficiency of about 45%-50%. On batch #2 (a dry stout), the efficiency was about 60%. On batch #1, I forgot to up the grain bill to account for extraction loss--I missed my OG by a bit (44 instead of 55). On batch #2, I upped the grain bill and hit my OG pretty close (48 instead of 50).

I know that batch sparging isn't the most efficient method; however, I don't want to be in the kitchen all day either. The trade off is buying more grain. I've read that you can achieve 70-75% extraction w/ this method.

I know I must be a procedural thing. Where should I begin? Or is my extraction rate typical of this method? In which case, I'll plan accordingly and buy more grain.

If anyone has experience w/ this technique, please lend your thoughts.

v/r
Billy Bock