I have noticed any time my cell phone is searching for reception, it wears the battery down pretty fast.
It used to be I had to be concerned with roaming, and that seemed to also make a difference in how long my battery would hold a charge.
I always remember people said you needed to let your battery go completely dead before you recharged it.
I don't think I ever did that purposely, but just charged my battery when it was getting low. I have never had any problems doing it this way.
Of all the different cell phones I have had, I have never had to replace the battery before getting a new phone.