My son has an Hyundai Ioniq 5 electric vehicle which has an internal VTL (vehicle to load) 240vAC power supply which can satisfactory power domestic devices.
Thinking of starting a small (light) system with just an Atom/Core with a SSD music store.
Suspect the battery drain should be low impact on km range,
Any thoughts ?
Get a wattmeter off Amazon for $20. Measure the average load from real usage on the Atom over a few hours of real listening. Then consult your car’s manual to figure out what sort of drain that represents over an hour. The consumption will vary according to speakers and volume, which is going to be area dependent also.
The use case puzzles me though. Is this for playing music when camping etc. or as a replacement to the car stereo? If the latter, I’d just buy a better car stereo.
Of course, you could just do it. Drive to the middle of nowhere. Hold a rave in the woods. If you driving home or hitch hiking home you’ll have you answer 
3.6kW, 15 amp rated. I’d have thought it was more than capable of powering that system.
You’ll need the actual usage to work out the effect on range/capacity, but even at 3.6kW it would take 20 odd hours to drain the battery from full to empty. And I’d be staggered if that system drew anything like that much.
One thing to beware of, the 12V battery needs occasional top up, there should be a utility mode you can use to ensure the main high voltage battery can occasionally top up the 12V battery if the car is unlocked and in use. If utility mode isn’t used, and the “ignition” isn’t on, but the car unlocked, then the 12V battery can drain. That happened on my Kona, not sure if the logic for the Ionic 5 is the same, worth a read of the manual. My car needed a new 12V battery after I accidentally drained it by leaving it unlocked whilst cleaning it.
…you might need to make a quick exit from your impromptu rave, which will be difficult if the 12V battery is dead 
We use a Ctek MXS 5 battery charger to keep our ICE vehicles 12v topped up, guess we may need to test if this can be used to charge the EV’s 12v from the VTL.
The VTL will be presumably powered by the Main Lithium batteries rather than the 12V Backup battery.
I doubt you will have much problems power such a low powered device (in comparison to what a car uses), although it sounds a bit overkill. How do you intend using it - is this an ICE system?
The Ioniq 5 is 100% EV, there is no ICE.
The 12v battery is used to unlock and turn on the vehicle only. All drive propulsion and VTL comes from the 84kW of lithium cells.
The usage of the proposed Naim system is for better sound either whilst travelling and also whilst picnicking/camping.
Literally and physically impossible to upgrade the inbuilt audio system in an EV, as it’s too tightly coupled to the car’s operating system.
In Car Entertainment vs Internal Combustion Engine
Sorry I was born a petrol-head
You’d plug a 12V battery charger into the VTL socket, and use that to keep the 12V battery topped up!? 
Fair enough. Under normal circumstances the car uses a 4 hour cycle to keep that 12V in shape, by charging it from the main drivetrain battery. You can tell by a little light on the Hyundai logo if this is taking place. The light also illuminates If the drivetrain battery is supporting climate functions triggered remotely.
If you open the car, but don’t “start” it, then all the electronics are running off the 12V battery and that cycle is interrupted. The electronics on my Kona easily draw 2-300W, so the 12V battery doesn’t last long under those circumstances. Turning on utility mode allows the drivetrain battery to charge the 12V battery again. When you’re driving, the 12V battery is kept topped up from the drivetrain battery. It’s only if the car is open, but not started, that you might have issues with the 12V battery draining.
I think! 
The ICE in the Ioniq5 is compatible with both Android Auto and Apple Carplay, which is also wireless making easy to use.
So why not just stream a radio or Qobuz, et al to the ICE?
DG…
Hope I never pitch my tent near you on a campsite!
But there’s no petrol.
I have to say, no matter how much noise they were making, if I pitched a tent next to someone running a Naim system off their car, I couldn’t bring myself to complain X)
Unless of course said system wasn’t on a proper rack.
In Australia, often an adjacent tent can be hundreds of km away….
95% of Australia is Crocodile Dundee territory - the internet is the gaps between crocodile nets and shark nets
Sound quality is inherently limited in a car, so to my mind it is highly questionable as to whether it’s worthwhile – and that is before you even consider whether you can get speakers in there that can do justice to it. As for camping probably great with headphones, though for the cost there are more portable alternatives that take up less space. Also I’d be hesitant of having something of the value of an Atom plus Core in a car!
I have considered possibilities for music when holidaying with a campervan: with lithium leisure batteries and inverter, powering anything would be no problem at all, but space is a premium, and certainly no room for any even half decent hi-fi speakers so I’d look at headphones. For that I’d probably use something like a Chord Mojo+Poly, or maybe Hugo+2Go+2Yu
Presumably having an Atom and a Core means you have to setup a network of some sort. Do you intend streaming from the internet? If not then might a USB stick replace the Core, and therefore reduce what you need?
I thought the core could be connected directly to a streamer, though it seems most people don’t use it that way
Not fully sure, but looking at the Atom spec, I think its USB input is expecting some sort of storage attached, e.g. Disk drive or Flash Drive.
I think the OP mentioned an attached SSD drive.
I’m even now struggling to visualise the use case. Will this be Atom and speakers in a tent, or Atom and speakers blasting out of the open boot of the car or what? Maybe a Muso would be simpler (only one wire so quick to pack up and flee when coppers descend on your dogging site).