In fairness, a friend of mine and I shot a reception where we both had 580 EX IIs on our cameras, and there were two 430 EX II slaves set up on opposite corners of the dance floor for 'light on demand' essentially (with both of us triggering both flashes unless somehow blocked). I never had to change the batteries in any of my flashes (though my buddy may have changed his once, I'm not 100% sure). I may not have delivered 3-5000 images, but between the two of us we darn well took that many..
Unless one is trying to light the entire venue and shoot at ISO 200, F8, speedlites don't get much of a workout at a wedding reception. If you're shooting manual on the remotes they are probably 1/8 power or less and the ETTL on camera is probably firing at even lower power since the subjects tend to be closer.
I routinely use an on-camera 600EX-RT and one or two remotes, each with a Pixel pac never have to replace batteries and when they go on the charger for the next job they are rarely even close to half down. My approach is to have ambient within 1 or 1 1/2 stops of "proper" exposure on the camera meter. Then have FEC 0 or -1/3 and ride FEC based on the tonality of the main subject. Having used packs, either Quantum Turbos or Canon or knockoffs for essentially every event gig, I can't imagine someone trying to do a job without them.
