NO! One of the dastardly tricks involves disconnecting the battery, even for people who simply want to replace it. There are experts who will argue with me, but I've heard too many horror stories about numerous computers locking up. A couple of mechanics said if the engine would start after the service work was done, it wouldn't come up off idle when pressing the accelerator, and it wouldn't come out of "park". The cars had to be skidded off the hoists and onto flatbed trucks for trips to the VW dealer to have the computers unlocked. Designing cars like that is not in the owners' best interest. In my opinion it is a "customer-unfriendly" business practice that makes money for the dealers. GM, BMW, and I believe Audi do similar things.
This information comes from a very high-level trainer who owns a shop that specializes in the one out of a hundred cars that no one seems to be able to diagnose. His customers are other shops around Chicago. He works with representatives from most manufacturers, and other instructors, then puts classes together to cover things like this and other types of diagnostic problems for mechanics from independent shops. If his information was wrong, someone would have corrected him by now.
To be safe, never disconnect the battery, and if you need to replace it, use some type of memory saver device. Some plug into the cigarette lighter socket and use a 9-volt transistor battery, but those only work on cars where the lighter always will work with the ignition switch turned off. I use a small battery charger with the leads connected to the engine block and the battery positive cable, but doing it that way runs the risk of a clamp popping off or the positive cable accidentally touching ground. Just have to be careful doing it that way.
Thursday, May 21st, 2015 AT 1:34 PM