Did you read the link in the post above you? I can almost guarantee that your battery doesn't drain any faster without using the app killer.
From the link you gave me
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I have seen some claims that battery life improves with the use a task killer but unless you are running a lot of network applications I don't see it happening based on the way Android is designed to let apps sleep. I know I haven't seen much difference than the reported life of folks that use a kill all task killer three or four times a day. Based on what I know about Linux I can safely say that I don't see any real reason for using a task killer to ever kill all applications on a Hero. You might gain a momentary bump in battery life by not having an app check something here and there but you would lose it again when you have to load everything every time you start an app. And the degrade that you would have in performance just isn't worth a few minutes of battery life in my opinion.
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These assertions are not consistent with my own experience using eris.
First off, I see absolutely positively NO degradation in performance from killing and restarting the applications. By the time I come back to an application, I don't remember what I was doing previously, and the time spent loading the application is small anyway. Every time I go to the browser, for example, I mean to go somewhere else.
One exception of course is turn by turn direction, but I have the option of not killing the browser at that point.
Further, charging my phone annoys me -- it will reduce the battery life (at least in all my past experience).
Secondly, I have in fact noticed that the battery lasts longer in the way that I use the phone now that I have started killing the applications as soon as I am done with them. My wife has an droid and I have an eris. We both noticed the increased battery life.
Manufacturers can assert whatever they want -- perhaps your experience coincides with that assertion, mine does not. By the way, I kill all applications as soon as I am done with them -- not just 4 or 5 times a day.
Personally, it annoys me to no end when my desktop is cluttered up with stuff I was using two weeks ago, like some people's machines I see. I keep only as many windows open as are necessary to accomplish the task at hand. I am quite flustered that there is no easy way to kill applications from the menu. The app killer menu is only a poor excuse for having designed the interface correctly in my opinion.