Depends on the mAh too..... My 5000mAh lipo lasts a typical 8am-3pm game and still has plenty of charge at the end of the day. But I'm thinking of switching to smaller 1600mAh batteries that will fit in my handguard, and I might buy three.
And for the sidearm? I usually end up using only a couple of mags at each event, and that's only when it's one of those situations when I'm pinned down and almost out of ammo. I've been to events where I never even pull my sidearm out of its holster. I don't bring much gas lol.