A friend of mine had the battery replaced under warranty. I've always had older vehicles where a battery replacement would mean resetting the clock and radio station presets. This was not the case with her Odyssey, the clock was correct and radio presets intact. Would that clock and radio have another backup source, like an on board lithium battery?

 

I was told typically a temporary power source will be plugged into the 12v receptacle to retain power to electronics needed it, likely that was the case.