Its not really a matter of being a believer... its not like its some anciient myth that being on wifi saves battery. The wifi radio uses less battery than the 3g radioI get great battery life because I have spare batteries charged and ready to take over.
I really don't use my Droid half as much as I use to, so right now I'm getting a day and a half use and only down to 60%. But I'm really hardly using it because my wife is home for the holidays and I stopped using it for just about anything else since I got the iPad. Navigation of course I use it for and it still is giving me a day and a half.
I'm becoming a believer that leaving it on wifi when you are in a wifi area is better then putting it on 3G as well.
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