Very true, capacitors can keep a charge for years. that’s why it is a good idea to shorten the connectors to discharge before handling them.
It wouldn’t surprise me at all if dash cams do not even have a battery but only a slow discharge capacitor. That would explain for the short life after disconnecting them from an external power.
For the purpose of running a dash cam, it’s really not a problem because mine are only active when I drive.
So, it would not record if someone broke into your car or hit it in a parking lot ?
It will if your cigarette lighter works with the engine off and you leave the power cord plugged in. You could also hardwire the power cord into a 12V supply that works with the engine off.
My Dodge Durango has two lighter plugs, one is always energized and the other only works with the engine on.
You need to use a product designed for use inside cars. A typical consumer product for home use won’t be tough enough.
That’s what dash cams are designed for.