I've been looking at these memory saver tools, they use either a 9 volt or
12 volt battery source. They plug into the cigarette lighter and maintain the computer, clock and radio settings when you disconnect the vehicle battery. I'm wondering if these things are safe to use without damaging anything such as the cars computer system. You would have to plug this thing in before you unhooked the battery so you would be introducing another 12 volts into the system. Would doing this be harmful? Which one would be better to use, the one that uses the 9 volt battery or the 12 volt? I appreciate any help.
Thanks, Dennis B