Well I have one, the kind that plugs into the diagnostic connector. I still lost the radio pre=sets thought. Powered it with a small 12v battery but I’m less than impressed. Maybe a cheap knock off, or maybe not in all the way. Next time think I’ll just use the battery at the battery connected to the battery cables instead like I used to do. Another $20 piece of junk.
Did you have the key on or in acc mode?? lol
Yeah, I’d be scared I would let the factory smoke out of something by removing the battery out of a running OBD2 vehicle… 
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Any of the aftermarket head units I’ve bought within the last … X? # of years seem to keep the presets no matter what. I’m guessing they’ve just had some non-volatile memory rigged in. I still haven’t had a factory system that keeps them though.
But I have wondered about whether or not I don’t want a memory saver to keep ECU memory alive. IDK…
I’ve been known to either write down or take pictures of the presets and put them back in for the customer…
But on a lot of the Honda’s the radio and nav would lock out and if you didn’t have the codes the customer had to go to the dealer to show prof in order to get the codes, PIA, so you got really good at using some kind of memory safer…
I remember the Hyundai’s and or Kia’s being the same way, and we have even had to wait for a code to come from Korea for a radio code way back when… I’ve waited a week or 2 to get one… started writing the codes down on the top of the radios, got really good at pulling radios for the serial number needed to get the code… lol
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No car was off. In the past I had used the 9 v in the cig lighter but the car has to be on to activate the socket. Everything came up again and didn’t have to enter the code. Maybe it just saved everything else, I dunno, but expected better. I just still think the best way I clamping a battery or charger on to the battery cables, but they are so short it’s hard get them to stay. Can’t remember what I did in the other car before. I’ll have to think about it.
Yes it is defiantly a KOEO thing, and if power is not coming out of the power/cig socket, power will not go into the socket, remember a circuit is a circle, break the circle and no flow either way…
When I had an Acura some time ago, each invoice for service from my dealer had the code printed on it, so I always had the code available. I don’t know if that’s still the case, but it’s worth keeping in mind.
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