Spiral, we do not advise using 13V wall power. As stated the higher car voltage is offset by circulating air that keeps the temperature down a little. so you end up about even
Another point is that LEDs are coupled with a resistor that is matched to the input voltage. If the unit were intended to run on 13V all the time we would put a different resistor in. The limired amount of car adapter use at 13V isn't going to be a problem, but running the unit 24.7 at 13V would probably decrease LED lifespan.
The other problem is the wiseguy who decides to try 16 or 17 volts. 'No, Tom, nobody would do that.', you say... Sure, bet me. It has happened, and surprise...the guy told me about it...
Thanks, StoneMonkey.