App save battery not working, can't turn off highlights the failure of the application or opens menu. After upgrading to Android 7 phone is slow, slow. Wi-Fi knocks or what not to do. After 40% charge the phone is not possible to use it, it is not possible to close and open the application to call the program saving the battery closes all apps.

If you would like, you can return back to Android 6.0, here is the link: http://www.needrom.com/download/blackview-bv6000-4/
If you are using Win10, you may have some problem to install this, please follow the below steps:
1. Connect your phone to PC's USB
2. Open folder C:\Windows\inf
3. Right-click the file wpdmtp.inf
4. Select "Install"