Just remember you can't use the batteries in the new 12v Simple Value Argos drills, they use some weird lithium chemistry that isn't approved yet. You could check with your event organiser, but it might be best to go with Nicads if you plan on using the drill batteries, most lithium ones aren't approved (aside from DeWalts with their a123 LiFes iirc). For reference, My featherweight has a 3.1Ah battery but that's just because I have an abundence of space and weight left.