is this battery drainage normal on NL820?

I've had several various android phones over the years, and Lumia 820 is my first WP phone. I've had it for months now and it was satisfying at first 2 months.

In order to increasing the battery life, I switched off the bulk of items like WiFi, Gps, etc and used them only needed, it worked, but recently I have suffered really fast drain on my battery even in battery saving mode--- lasts 7-9 hrs from almost 100% to 0% with moderate use. If I unplugged it moring, 3 hrs later almost half of the battery is drained, this is unacceptable!

Not sure the exact reason. Can this problem be solved if pop in a fresh one?? I already ordered a new secondary one from MPJ. Anyone have similar exp.?? Is this a normal drainmage after several months usage or my stock battery just going to died??

I think this is a WP Phone bug n not sure about the reason also, I personally switch a new one and the world change since then;)