Mine lasted just a tad over 3 hours most recently. At about 2 1/2 hours I would get the low battery warning on the right one but then they seemed to even out before they would die.
Mine were purchased in December 2016 and they're down to about half an hour now almost 2.5 years later. I've thought about trying to get Apple to run whatever diagnostics they have for AirPods and see if they'll replace them, but in real life lithium batteries do lose capacity with age. I'd be very interested in feedback from other early adopters on battery life.