The battery itself might be faulty. or the battery terminals could be corroded. Just make sure the terminals are clean. You can also just hook the battery to a battery charger and make sure it’s fully charged. Then take it back to the dealer and get a proper load test done on the battery.
There is no guarrantee that a new battery will not be faulty. We manufactured engine driven machines at my previous job and from time to experienced problems with brand new batteries which were faulty right from the start.