Is a battery replacement enough reason to keep my current phone?

The repair counter quoted $96 for a battery service. My brother pointed to a refurbished phone for $390 and said, “Why put money into the old one?”

The old one is an iPhone 13. Its battery-health screen shows 79% maximum capacity, and lately I carry a charger to afternoon classes. The camera, storage and apps still suit me. I had not been shopping for another phone until my brother sent the listing.

Apple explains that maximum capacity compares the battery with when it was new and that an aging battery can mean less time between charges. That makes a service worth asking about, rather than assuming the whole phone has become useless. [Apple's battery guidance](https://support.apple.com/en-us/101575).

I know a new battery would not make every component new. What else would you check before spending the $96? I want to make a sensible repair, not defend keeping this phone purely because I already know where everything is.