At what point should you service the battery?

My Prius just turned 185k and is on the original traction battery with no issues so far. I have noticed my mpg has slipped a small amount but the car still averages 46 mpg. I have never used the Dr Prius app to actually test the battery but I see a lot of post in which people are balancing their cells and that seems to give the battery new life. As well as cleaning or replacing the copper terminals that corrode over time inside the traction battery. Is this maintenance that should be done preemptively or should I just wait until I get the red triangle? If I’m still getting pretty good gas mileage do I stand much to gain in mpg or longevity if I serviced the battery now? Thanks