Hi papa381,
Welcome to Apple Support Communities. I understand you're experiencing low battery life performance, along with the inability to use Face ID on your iPhone. I can help point you in the right direction.
I recommend reviewing the battery health section of your iPhone to help determine if the battery needs to be replaced. For additional details on how to determine this next step, please follow the section of this helpful article that says, "Battery Health": iPhone Battery and Performance
Now if the battery health is in a good state and there's no indication that the battery needs to be replaced, I recommend adjusting the settings on your iPhone to help improve the battery life. Here's the proper steps on how to perform these steps: Maximizing Battery Life and Lifespan You'll want to specifically follow the section that says, "Tips for iPhone, iPad, and iPod touch."
With troubleshooting Face ID, I encourage for you to follow the steps outlined here: If Face ID isn't working on your iPhone or iPad Pro Following these steps can help resolve the ability to rely on using Face ID.
Best regards.