For those considering an AW Series 2 to use as a running watch sans iPhone, here are some preliminary stats on battery usage – Did this week's long, slow distance run @13.5 miles in 2:13:29 (9'52"/mi) w/ iPhone turned off completely. GPS and Music through bluetooth were on. Battery drained 60% (from 78% to 18%). Only unusual factor was a lot of screen glancing because I was trying to keep my pace about 1'30" slower than marathon pace (though I bonked the last few miles). Hope that's helpful.