Which is the best app to save battery of a smartphone (like battery doctor)?If you have an Android Phone, trust me on this one! DO NOT USE ANY BATTERY SAVER APPS!
You can't get free energy from the universe or something, and adding an app which consumes more ram and battery to "save battery" sounds ridiculous. What they basically do is app management or memory management. You can do that yourself
Don't run apps in the background all the time, and if you want to save tons of battery, here's a tip
Uninstall Facebook and Fb Messenger app, and use the mobile version of facebook via chrome (the newer version of android chrome has notification support as well, so enable it and it kind of gives similar experience as the fb app, with no excess load on the phone.) This hack improves battery dramatically. You'll be surprised to see how much battery Mr. Zuckerberg took by spying on every single thing about you 24x7!
[Warning: EXPERTS ONLY] If you want more effective battery saving tips, ROOT your phone, and find an app disable/freeze tool from playstore. Use it to disable Playstore app (or Vending.apk) and Google Play Services app. (This is a system app and is there on all phones running Android) Some apps need this to work properly, so enable when required and disable when you're done. Simply disabling these two apps doubled my battery life, phone ran like it's on steroids!