Life ECU battery

just a note, the ECU has its own back up battery. It is a rechargeable battery. 

A good practice is to power up the ECU once a month, doesn't neeed to run, just put some power on the ECU. 

I failed to do that last winter, while I renovated my bodywork. The first event the ECU had lost all it's memorized data, engine total time and the real time clock (RTC) was gone. The battery can be changed and the RTC reset only by a RPE service center. 

So just power up the car once a month and avoid draining the ECU battery.