I wouldn't mess with Task Killers.
In regards to battery apps I do not have any experience on them.
I don't use them.
Somebody may chime in here that could possibly recommend some though.
I've tried several battery status apps and a couple of task managers and not seen that error, but most of those other apps I have not tried.
I find a task killer useful when I have to stretch out my battery time, but I don't go nuts with them...do you really think they are harmful, cereal killer? A lot of people seem to use them.