Here are some tips and tricks to help your Priv battery last longer, but do change the battery if yours is old:
First thing to do is enable developer options by going into phone settings and then "About Phone" and tapping "Build Number" 8 times until it tells you that you've become a developer.
Then, back out of there and you'll see developer options at the bottom.
Go in there and scroll down to the three animation settings which will all be on "1x".
Tap each of them and lower them to "0.5x".
Then, go back out and into "Storage" and wait for the "cached data" to load. Most likely there will be at least 1gb of cached data.
Simply tap it to clear it and wait a few seconds.
After this, you should see an immediate performance gain.
-Lower the resolution with adb to 1080x1920 (see here
https://forums.crackberry.com/showthread.php?t=1093326 )
-Keep Bluetooth/WiFi and scanning OFF unless in use
-Disable all BB Hub+ and the other BlackBerry apps
-Disable ALL the Google apps that you don't actively use, especially the "Google" one. I would use Google Keep, Google Contacts and Google Calendar, those are not resource hogs
-Avoid using Google Maps or do any navigation unless necessary
-Don't play any game that requires more GPU power than a simple 2D game like candy crush
-Don't use the Full Facebook or Messenger app, use Facebook Lite and Messenger Lite instead
-Keep the brightness at 50% unless necessary
-Enable power saving mode all day
-Connect the phone to a Wi-Fi especially when signal is weak