That explains a lot...I just tried the WiFi on my phone a few days ago and next thing I know, I have almost no battery power when I had more than half a bar when I started. I pay for the internet on my phone, so the WiFi isn't really necessary for me as long I have a signal.
I also changed the setting to Automatic on my phone brightness and I noticed a big difference with that. I used to run out of battery by the end of my work day, but now I have most of my battery bar left. Another thing that helped me, was when I changed my apps that auto-update (like my Yahoo email app) to not. I changed my Yahoo app to not notify me each time I get an update. In my case, I don't need to know about each and every email I get. I only change it to notify me, when I'm expecting an important email.
Another thing you can do is change how long your phone's screen will stay on when not in use. 30 seconds was fine for me, vs a minute.
Also, remeber to close out of an app when you are done with it. Ex: Google Maps. It will really eat your battery power unnecessarily if you aren't using it, but it is still open with navagation on. Change it to off, when not in use.
I've had my Droid Eris for a year now! I still like it a lot!
