Sorry I can't be of any help but I know what you're going through. I upgraded to the Epic 4G Aug 12th and in about 3 weeks I've had to exchange 5 phones because Sprint could not fix any of the ridiculous amounts of basically unique issues with each phone. One time a "Tech" had me do all kinds of resetting, punching in codes in my phone and then basically he did some kind of reset from his end and all of a sudden I noticed my battery went from around 90% battery life to less than 20% and he couldn't explain why that happened. I've been a long time loyal corporate customer of Sprint since they were Nextel and push to talk was the coolest thing going on but as the years pasts on they just seem to care less about customer satisfaction.
I will be coming up on about 30 days and 5 phones since I upgraded and even though I finally took matters into my own hands and did research on the web to try and make my phone more stable, I am still constantly having to power the phone down, remove the battery, SD card, soft and hard resets I'm still having issues that are not satisfactory. The last person I talked to said he wanted to get his supervisor involved and what they told me was that the best they could do was give me an even swap for the Epic 4G to the Google Nexus S 4G or the HTC Evo 4G. The other choices were downgrades so I didn't even want to consider those. The point is I purchased the Epic because of how great the phone looked in the specs, the great in my opinion AMOLED screen and the option of having a nice sized slide out keyboard. Basically its works great about 40% of the time and the other 60% I'm trying to get it to be a smart phone again which is not acceptable. The Nexus price on their site retails at about $549 and the Evo $449. The Epic is at $499 but so is the new and improved Epic 4G Touch so I asked why I couldn't just have the improved phone I purchased in the first place. I'd just be missing the slide out keyboard but I could live with that. Of course that was a no go and and told the guy I would need to think about it because I really don't care for the Nexus or the Evo. I either want a working Epic 4G or the new Touch. He said he would call me back tomorrow and I could give him my decision. Wouldn't you know it, I never got a call back.
I'm about ready to leave Sprint and go with another service provider if they don't make a satisfactory resolution. It's like they are punishing me because Samsung just happen to send 5 bad phones to the store in my area. I've lost faith in Sprint and I think I'm ready to give another provider my money. The worse that can happen is I'm not happy with them as well.
Sorry about the rant and no solution to your battery issue, but I just wanted to let you know I also had a weird battery experience. I hope Sprint takes better care of you than they did me for the last month. I do love the Epic but its turning into an Epic failure.
Jim