Thanks for the tip Farfisa, I'll invest in one.

They're not 'that' pricey, a multi-purpose charger is usually around $20 with a few AAs included, and you're right they don't last forever but so long as you swap them out between uses and always start with a fresh one you shouldn't have any hassles getting through a set. Like Farfisa mentions a Onespot or some other daisy chain option (like a 5-spot adapter cable for BOSS tuner pedals) is the greatest thing for pedals that all have appropriate jacks.

So what exactly is the difference in a phaser and a univibe?

It would depend on the manufacturer's specifications in each unit but from what I've always read the main difference between any 'swirly' pedal like a phaser, flanger, chorus is the scope of the potential range for the envelope filter. It's differences measured in milliseconds.

Pretty sure the main difference you'd notice is that a phaser tends to be more subtle while the univibe (if I remember correctly) is closer to a chorus and a more prominent effect.