I've had my phone for a couple weeks now but I don't make too many voice calls. Right now I'm down to 40 percent battery after a day of pretty heavy usage but I've only made a few calls totalling 7 minutes in all. These calls have used 7% of the battery according to the battery usage. I've been in great service areas and I just didn't expect calls to use this much power. Is something wrong or is this normal?