I have a new "memory saver" that attaches a 12V power source (e.g. Spare battery) to the car's OBDII port during a battery change to save radio presets, PCM "learning" and the like. This seemed like a "no-brainer" and a smart thing to do but I see conflicting advice on, you guessed it, the Internet: some sources say it's prudent and almost essential but other say it's dangerous. What's been the exprience here? Thanks.