Good Day jbeck,
Your check engine light shouldnt come on just in AWD for your battery if its showing 12 volts on a multi meter and 11.5 on the cluster. If it was your battery your check engine light would be on all the time. Im thinking that it would be more along the lines of an electric sensor in your AWD system. I would say your best bet is to take it to a dealership and have them do a complete tear down on your AWD system.