MacBook Pro Overheating, Loud Fan

When Apple replaces the battery on a Retina model laptop, the entire Top Case Assembly is replaced so this means everything on the laptop is removed for the repair. I have no idea what an Apple tech will do with the fan, but I know I always clean things up as I repair a computer (especially if the item is already removed).

Most overheating issues are caused by software issues. To look for possible software issues run EtreCheck and post the report here using the "Additional Text" icon which looks like a piece of paper.

I'm assuming the hardware is Ok since you just had Apple repair the laptop and they would have run their service diagnostics to confirm the hardware is working. The diagnostics do a good job of identifying hardware issues with the cooling system. If this is a new problem since the battery replacement, then take the laptop back so Apple or the AASP can make things right.

Are you using any kind of case blocking the vents? Please see these recommendations about fans and fan noise:

About fans and fan noise in your Apple product – Apple Support (UK)

Maybe something else is causing higher fan activity:

Has there been a change in software settings (like energy saving) causing higher cpu usage?

You can try to enable the fan-activity-reducing low power mode:

Save energy on your Mac – Apple Support

You can try to identify CPU-consuming tasks:

View CPU activity in Activity Monitor on Mac – Apple Support

If you want to verify the installed battery, you can check its details:

Determine battery cycle count for Mac notebooks - Apple Support

Regards