Hey D'arcy Willett,
We're glad you thought to ask Apple Support Communities about the issue you're having with the ringer volume and battery life for your iPhone 12 mini. We definitely want to help! For the ringer volume, see if these steps help: How to put your iPhone on vibrate, ring, or silent mode
First, you'll want to ensure that you have the latest software version installed as this can help with battery life. If updates are needed, be sure to back up first:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Update apps or use automatic downloads
After updating, check battery suggestions and implement those suggestions, as long as they suit your needs. To see the suggestions tap Settings > Battery. You may see items such as reducing the brightness, and turning on Auto-Lock. More tips on increasing battery life can be found here too: Maximizing Battery Life and Lifespan
Another good idea is to check the battery usage to see how apps are using the battery, and if any steps can be taken to help. More details can be found here: About the battery usage on your iPhone, iPad, and iPod touch
You may also benefit from Optimized Battery Charging and Low Power Mode. More details can be found in the following guides:
About Optimized Battery Charging on your iPhone
Use Low Power Mode to save battery life on your iPhone
After updating and implementing those tips to maximize performance, fully charge your iPhone, then use it normally to see if you notice an improvement.
Keep us posted on the results.
Take care!