Smartphone keeps crashing?

My Huawei P Smart (2017) just crashes when opening some apps and goes from 65% battery to 2%. Why? I don't want to buy a new one

1.First reset the device to the factory setting.

2. Then install app for app app. New setup not backup, the errors can't be played back again.

3. If found "stubborn" app that no longer use.

4. Otherwise, really assume a device is defective and apply warranty and repair or exchange.