It doesn't show up as free on the play store, but it is only $1.49 so fairly inexpensive and worth checking out. From the description it works like the pegasusq governor which puts a core to sleep when not needed. If you happen to be running stock rooted with the AGAT kernel you can accomplish the same thing by selecting the pegasusq governor with an app like voltage control. I know this governor did save a lot of battery as it would keep the core asleep until needed so when just reading an email you weren't using the second core.

Codegerm

 

Same here, I have had success with underclocking.

I try to limit the number of apps on my phone to avoid any virus types.