Shutting down and Flashlight intermittently not working

A friend of mine has a iPhone 11 and is having issues where it shuts down every once in a while and has had issues with the flashlight not functioning. I was considering a battery replacement, but I am unsure if that is the best first step. I have the skills to do so but would like it to be a one and done repair not something I have to go back to if a new battery doesn't fix it. Any thoughts would be appreciated! Thank you!

Edit: He had the battery replaced on it about 2 weeks ago due to it shutting off etc. but the problems are still happening. Please advise.