You can get those 9 volt battery deals to plug into your cig lighter for just this purpose of saving radio codes and other memory functions.
Advance auto used to have them, but you can find them on the web.
Those work fine for short term, like maybe 24 hrs., then the little 9 volt battery is drained. Their really just to be used when servicing the vehicle because you don't usually have the battery unplugged long. If his is feeding back and energizing the fuse panel like he says it'd be lucky to work at all.