Hello Tim Swope,
Thank you for using Apple Support Communities! I understand that you're experiencing an unexpected battery drain and use of the fan on your MacBook Pro after upgrading to macOS Catalina. Having your battery last as long as possible is important, and I would be happy to help.
The battery drain and fan usage could be related to each other so I would like to start by seeing if we can further isolate potential causes. The next time the fan starts randomly, let's check the following:
- Determine which graphics processor is in use at the time: Find out which graphics processor is in use on your MacBook Pro - Apple Support
- Check for unusually high CPU activity: See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support
I would also like to have you reset the SMC on your Mac, then test if there's any change to the battery usage or fan:
How to reset the System Management Controller (SMC) on your Mac - Apple Support
If you're still experiencing the behavior, here are some additional steps to take next:
About Mac notebook batteries - Apple Support
Cheers!