Our Shure IEM body packs are battery-munchers, and I've been caught a couple of times leaving the input jack connected to a couple of my pedals that I power with PP3s (some of my pedals are a bit noisy if I power them with a mains adapter) - and of course, next gig - flat battery.
It crossed my mind to try rechargeables again, but I've never had much luck with them - only 8.4V at full charge (which causes all kinds of weird behaviour in some kit) and they just don't last.
What brand PP3s do you use and do you put fresh ones in before every gig ?
I suppose it's about getting the capacity right - there's no point in spending on a premium battery that will only make it through one and a half gigs if you can get one for half the price that will make it though one full gig but no more.
Lack of planning on your part does not constitute an emergency on mine.