You won't necessarily need to return to the dealer for a warning light, but your computer will certainly dump all memory and you'll have to re-program some things, and your CPU will have to re-learn your engine-management.
I usually remove the batteries from my classic cars, and trickle-charge on a shelf, because there's no electronics to worry about keeping "perpetuated".
But my Porsche I simply leave the battery in-place, hooked up, and plug in the trickle charger... There's really nothing to worry about, the chargers have fail-safes built-in and will shut down all current to the car and from the car in the event that anything falls outside of certain parameters.. Kinda like worrying whether you'll self-combust.. It's been known to happen, but are you actually going to trouble yourself and carry around a fire-extinguisher everywhere you go? "Hey, dude, what's with the fire extinguisher?"... "I carry it just in case I self-combust..".... "Ohhhh.....".
Lastly, don't know why anybody would go to the dealer for a new battery. Got mine at Car-Quest for less than half the price of the dealer, installed in 5 minutes, and it was identical in every respect to my O.E., including the vent fitting. They actually charge you an hour's worth of labor at the dealer! I'm decently well-off, but I'm not stupid... ;)
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If you've got an issue, here's a tissue...