I first thought it is the battery performance, but once I had to restart the device to change the phone language, the battery actually dropped from 100% to ~70%. Later on I tried the same thing after a "full charge" for a couple times, and ended up the same. So that kind of explained why the battery won't last. I've been using the device for a month now, should I send it to repair? Or is there anyway to calibrate the battery? Thanks.
Calibration is done by running down the battery as close to empty as possible and then charging it to full. Care should be taken not to drain the battery below the critical level which could render it unchargeable.