My wife has the "unfavorable driving profile" in the e93 along with the seemingly "always on" iPod in the armrest. She would get the "battery drain" warning message with the jack icon, and even rec'd the "increased emissions" error.
Battery Tender or the Battery Tender Jr. will do the trick. Once a week overnight and even every two weeks will do it, and it made all of the above errors go away. The lighter is not powered, so forget that option - use the alligator clips under the hood on the red terminal and on the bolt to the left and front of that. Guy with the "hood up" reminder is right so you don't pull out with your junk attached.