Phone using almost double battery for voice calls than before.

[taylormah]

So I got the ICS update, and went through a series of factory resets in hopes to fix this issue but resets didn't help it. The issue here is the battery usage of the device for phone calls. When I bought the phone last year when it was released, I calculated that my E4GT was using 12% of the battery per hour that I was talking on the phone. Currently, even before the ICS update, it is using about 21% of battery per hour for voice calls, almost double than before. I thought that ICS update or a factory reset would help it, but neither one did. I can't account this to poorer signal, since signal's always been about the same strength all this time at my location. Any idea what could be causing this and how this can be fixed?