Went to do some Christmas shopping and the DTS was starting kinda slow, even though I've been keeping the battery topped up on a maintainer periodically due to my limited usage right now. I had a 'new' (1 year old) AC Delco battery, the correct group 79 (which is really obscure, only a handful of GMs used it), on hand, so I figured I'd swap it out proactively. Battery is under the rear seat in the DTS, so I was not looking forward to it, but I was surprised....Keeping the battery in the car has some merits; all the connections are nice and clean, as is the hold down, so no corrosion or dirt to deal with. I used a booster pack on the jump points under the hood to keep the car powered up during the swap too, so no need to reset everything. 20 minutes flat, including getting the battery and tools out.
Starts great now, and I have peace of mind knowing it's got a fresh battery. Old battery was an Interstate dated 2015, so not terribly old, but probably due.