Joseph has an LG Nexus 5. Leo says it was a really good phone. It hasn't been having very good battery life with Marshmallow, but it seems to reboot by itself. Leo says that points to a hardware issue, but it may also be a bad upgrade. He advises doing a complete factory reset. If the problems persist, then it's definitely a hardware issue and it's time to get a new phone.
How can Joseph backup his phone? Leo says it's not a big deal, Google will secure the apps for him, but he'll want to enable the backup to Google option in settings. He should do that first, and then reset to the factory state. Then run it for awhile without any other apps. If that works OK, then he'll know it's a bad app.