Battery will not be warranted... if you take it to the dealer you will get 'trapped' into the new battery... you'll be on the hook for an hour or two for diagnosis, then whatever they want to bend you over for on the battery.

Battery MAY test good if you go to an autoparts type place, at 4 years I'd just buy a new battery and toss it in- then, if there are still issues go to the dealer.