12V Battery: replace or wait until it fails

I just purchased a 2012 Prius C One with 138k miles. Loving it so far. I have most of the maintenance records from the previous owner, so I'm planning maintenance to do this spring. It doesn't look like the 12V battery has ever been replaced. It looks like it'll cost $250 to replace it, but I'm not having any issues, even though the car is 12 years old.

Is it worth me replacing it or should I wait until I see some signs of it deteriorating? And on that topic, aside from the electronics not coming on when I turn the key, what would I even look for to see if the 12V battery is deteriorating?

Thanks!