I had the same problem with the battery draining on my 2017 Transit as other forum users .Followed the recommendations listed on the forum but still had problems .After going through 4 batteries I decided to take the van to an auto electrical shop.They searched everywhere for a short or drain and finally found a tracking device attached to the main computer. The van was originally sold to a business and I assume they added that option.Device was removed and no problems now.
