Why is my brand new MacBook Pro battery running so hot?

The Apple Retina laptops run much hotter than older models. Depending on what you are doing the CPUs typically run between 50C and 100C with most average workloads running the CPU around 80C.

Run the Apple Diagnostics to see if any hardware issues are detected. This should tell you if the laptops cooling system is performing properly.

To look for software issues that may cause your laptop to run hotter than normal you can run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

You can try an SMC Reset as well.

Any overheating is usually from a software issue or a user not being prepared for how hot these new laptops run. Laptops really are not made to sit on a lap anymore.

How hot is "so hot"?

Suggestions:

Reboot to clear any stuck tasks which might be eating processor cycles.

Open Activity Monitor and give particular attention to the CPU and Energy tabs. Look for anything which seems to be using a disproportionate amount of CPU time or energy.

Are u talking about macbook pro 2020? Intel or m1?

The OP mentions a 2019 16” MBP.