I think I agree with the post above that said replace the battery. By the time you take it to a mechanic you will have paid for a new battery.
I've owned many, many new vehicles and I've never had an OEM battery last more than 4 years (if I kept it that long) with the exception of one. That is my 2010 Toyota 4runner. The battery had never given me an ounce of trouble but I replaced it 4 days ago because it was over 4 years and I don't want the trouble of a dead battery when I don't expect it. My 2003 Ram 1500 was 3 years old when I went into the store on a 105 degree day and bought about $90 of fresh fish and seafood. Came out and the truck wouldn't unlock with the remote. Used the key and it wouldn't start. The truck was already roasting hot so I called Enterprise rentals, they came and got us and I rented a car overnite so the fish wouldn't spoil then came back the next day with a new battery....don't need that stuff.