I purchased 2015 Honda Accord 7/19/2020 my battery...

I purchased 2015 Honda Accord 7/19/2020 my battery went out 9/12/2020 at a gas station i left my hood and see that battery is missing cap so i contact the dealer about it they say buy one and they'll refund my money ,so i ask did you service the car before you sold it to me and they said yes but my oil life is saying 30% iv'e put 3000 miles since i brought it 30% at 3000 miles when service manager tell me they go 6000 miles which one is it. For any one that buys a USE car know that they don't service the cars before they sale them to you