Task killers really only help when you're using badly written apps.
Yes, you might see improvements to battery life/performance/etc. when you run them, but any improvements disappear the next time you use the app, and in the mean time you might find some adverse effects from using the task killer (e.g. apps that provide updates on a timed bases may stop working because the task killer has killed the background service they use).
A better solution would be to look and see what's eating your battery and look for some settings or the developers email address to try and reduce the load.