That's likely not a kernel issue (unless it just started happening). Is your phone sleeping? Are you using the phone that whole time? If the phone is idle most of the time, and it still dropped that much, I would look at other things before looking at other kernels. What kernel are you on now? Does it do that with everything you've tried?
Assuming your phone is actually idle for a good part of that time, install spare parts from the market if you don't already have it, plug the phone in for a second, unplug it, then let it sit for a couple of hours. Open spare parts, then select battery history. What % does it have for running? After checking that, select partial wake usage for the top drop down, and verify that the second drop down says since last unplugged. What do you see at the top of the list, and what % does it have?