When running a race car with a battery disconnect, the ECU loses date & time when the battery is disconnected. I like having the datalogs date & time stamped and it's not always possible to grab the computer to resync the time after the power is turned on in the car. Not to mention the numerous times one of the crew turns off the power or it gets accidentally bumped.

I'd like to wire up a 9V battery with a diode (to prevent it getting cooked from car power) to retain the memory. Would this work? I'd also put a diode on the main power line to the ECU to prevent the 9V from trying to power anything else in the car. Would this work or is there a better alternative?
-Greg