I saw a guy post about his battery usage meter being blank on a jailbroken phone--I am experiencing the same problem with a non-jailbroken iPhone 6 128GB on iOS 8.1.2. I can fully charge the phone to 100% and seemingly at random when I check the battery usage it shows usage and standby as "---" and reminds me "Usage times will be shown after iPhone is fully charged". I am not plugging into iTunes or partial-charging it when this occurs...the phone has been fully charged and it just seems to lose its mind when it comes to tracking the battery usage. Any suggestions or has anyone else seen this? It seems to be happening a lot lately and not just since the upgrade to 8.1.2. Thanks!