Avast Battery Saver is a capable app which extends battery life by stopping apps which aren't being used and optimising device settings.
You can use the system on demand, opening Avast Battery Saver when required and tapping "Stop Apps" to stop everything. If you're unsure whether it's worthwhile, an alert shows you how much time you have left and how much more you'll gain by going ahead.
Battery Saver can also manage your device automatically with its customisable profiles. You might allow just about anything to run at home, for instance, but turn off all but the most important features for the "Night" profile, and cut your system to the bare minimum with the "Emergency" profile.
Alternatively, set Battery Saver to the Smart Profile and it automatically adapts its settings according to your usage.
Fixing a number of bugs.
A useful and effective battery saver app.