Sub Prime means loans to people who can't pay it back....basically. Sounds like you may have a bad ground somewhere. It's possible the new battery install may have sparked and killed a transistor inside the brain box, but more than likely it's just lost it's memory. Do you/can you hook it up to a scan tool? Look for codes, or no communication, probably worth you while to take it to a beemer shop and have them diagnose it before you spend big bucks.