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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When we bought our Hondas there was a card in the glovebox with the code on it. You can also get it from the Honda website. If you’re going to exchange batteries, make sure you have the code first. IIRC you have to be a registered owner, log in, and then recover the code.
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Some Hondas had the radio code on a sticker on the glove box door
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But just like wheel locks and owners manuals, customers loose them or they are not in the used vehicle when bought, yes finding the card is aways a nice find, just like finding the wheel locks… lol
Funny thing is, I haven’t seen to many factory radios being stolen, aftermarket yes, OEM-not so much… Maybe in other parts of the country, but not around my area…
To answer the question of can you disconnect the battery and use the lithium Ion jump pack? Absolutely not. You could do it with and old lead acid jump pack, but not a lithium ion jump pack.
The reason is that lithium ion batteries have a very low internal resistance compared to a lead acid battery. If the charging device isn’t calibrated for a lithium ion battery, there is a very high risk of starting a fire. One of the main reasons that lithium ion batteries catch fire so often is that the wrong charger was used.
Also the very low internal resistance of the Lion battery could easily burn out the diode pack in your alternator. The voltage regulator will not protect it because it is designed for a higher internal resistance and will see a Lion battery as a dead short.
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Every lithium-ion battery jumper that I have owned disconnects automatically after cranking the engine to prevent current feedback from the vehicle. Have you ever used your battery jumper? It won’t catch fire.
I have, but mine is old school, lead acid and I don’t leave it connected once the engine starts. I have never owned a L-ion jumper but what I said about L-ion batteries is still true. You have to be very careful with them.
On the subject of the Li-on jumpers, they’re mostly sold to jump cars. I have one, and I’ve also wondered about using them to jump small engine batteries. E.g. my law tractor, or generator. They’re both 12V, and I can’t imagine it would be a problem. But I don’t know enough about batteries or those jumpers. Anyone using them on small engine 12V batteries?