It's decent, but using it in outdoor running mode (the only exercise mode I've tried) depletes the battery quite fast. I enable the optional GLONASS, I'm not sure how much effect that has.

Big handfuls, you'll get about 8 days out of it, less a day for every 30 minutes of running.

Garmin have released a few firmware updates for the watch which may account for the difference between my findings and those of early adopters.

GLONASS on most devices that speak both is enabled only when GPS signal quality is poor enough, and it just uses it to improve the accuracy of your position.

It uses more battery life, but in a lot of cases it's the difference between accurate positioning and not.

So, yeah, I'd try doing same day runs on clear days, with GLONASS on and off, and compare drain rate.

To be honest, it doesn't bother me enough to run any sort of rigorous trial. Going by some trusted reviewers, GLONASS sucks an extra 20% during activities. I'm never so far away from being able to charge it that such a small difference bothers me.

It lasts atleast 2-3 days, honestly I charge it every other day and run 3-5 days a week and it works great.

I'd guess it depends a lot on how much you use the GPS. I've had mine for about six weeks, and I charge it once per week.