Motorola RAZR V3C Battery

I have a Motorola RAZR V3C and lately I've been noticing that the battery goes dead (from a full charge) every afternoon. I bought a new battery since I thought that the one that came with my phone may have developed a "memory" but that one does the same thing. I think that it has something to do with the lack of signal available inside the building where I work, or perhaps it's constantly searching for an available network, so yesterday I tried turning the phone on "Home Only" network setting and the battery lasted all day until 10 PM last night. I don't really want to have to keep switching between Home and Automatic networks - has anyone else had this issue? Is there a way to put the phone in powersave mode?