Strange cell phone problem with the battery

While working at my job, I would often put my cell phone in my small locker provided to the employees at that place (it was turned on, but put on silent). When my shift was done (My shifts are generally 4-6 hours long), I would get the phone, only to find out that the battery was really low (despite being fully charged when I put it in. In one case, I even recharged it overnight before putting it in the locker). I tried putting the cell phone on top of a folder (so that it wasn't physically touching the metal), but it still loses all its power.

Thinking the lockers might've had something to do with it, I kept the cell phone on me (we're not supposed to carry them while on duty), and left it on, but on silent mode (so any calls I get don't vibrate or make noise for me). For some reason, when I'm carrying the phone in my pocket, the battery doesn't lose any drainage (nor does it lose power while lying on my wooden computer desk). It still has three power bars on the battery icon when I'm done with my shift while it's in my pocket.

So my question here is, are cell phone batteries prone to draining if it's exposed to metal or something? I have a Sprint phone, Sanyo MM-7500, but my old cell phone before this one never gave me any battery issues. I'm just wondering if I discovered some kind of flaw in the battery, or if it's a known issue (the battery seems fine as long as I don't put it in my locker at work).

I'm thinking of emailing Sprint about the problem, but again, I'm not sure if this is a known issue already, or if I discovered a problem that they're not aware of.

Any of you ever have any kind of problem somewhat like this?

Jam it back in, in the dark.

Cool replies, yeah I think that might've been the problem (the "searching mode"). I went to the Chicago Museum of Science and Industry today, and saw that it was doing that "searching for network" thing, so just turned it off (and I have to say, I don't think I want to go back there anytime soon. It's not the museum, which was pretty cool, it was the horrendous traffic, which I'm not used to driving in, but I'm going off topic now ).

Yeah, I didn't think anything was wrong with the battery, or else it should've kept dying even while I had it on me (and not inside a metal locker). And I'm sure that'd be an easy enough problem to solve if it was just the battery nearing the end of its life (I just got the cellphone about 2 months ago).

There's nowhere I can't reach.