Welcome to Android Central! Charge up to 100%, then let it drain to 20-30% with normal usage, without charging in between. Then show us:
1. The main Settings>Battery screen.
2. The fullscreen battery graph screen (which shows Awake time and Cell Signal Strength).
3. The Screen category (to see total Screen On time).
4. The Cell Standby category, if present (to see Time Without Signal).
Is there a menu that shows how your mobile signal has been? It's usually part of the graph--can you tap the graph and make it fullscreen? Poor mobile signal can eat up battery.