I know that power is constantly supplied to the thing, but of I just have the adapter itself plugged in with the car off, nothing charging off of it, will that drain the battery too?

 

It’s been known to happen, plus the adapter can overheat.

 

Depends on the adapter.

An inverter does not draw if it is turned off, but does any time it is turned on, with or without a load, since it is producing heat energy if not DC energy. If it has no on/off switch it is drawing when plugged in.

A simple 12VDC/5VDC doesn't. That is just a resistor on 1 leg of the circuit. A more complicated circuit would draw.

 

I leave my phone charger plugged in over night but it does not drain the battery. If that is what you are referring to, I would recommend having your battery tested.

 

Agree, I leave my phone charger plugged in at all times. Sometimes the phone is plugged in, usually not. I've never had any problem.

An AC adapter, though, may be a completely different thing.

 

ooohhhhh my bad. Missed the "AC" adapter. When I was truck driving, I always unplugged mine because it did drain the battery on my semi after a few days because it is constantly converting DC power into AC power at the ready, it does not necessarily "store" that power and hold it like a battery would. So yes, I would definently unplug it while the vehicle is not running.

 

If it gets hot it is using energy. Inverters have heat sinks for a reason.