How is the Nvidia Shield with OTG + charging though? Sure the mini HDMI can be used for the audio, but unless it can also support a USB flash drive, steering wheel controls etc it becomes difficult to use in a car. Although, I believe the Shield tablet has a MicroSD slot, so that rules out the flash drive, using HDMI would I believe negate the need for a USB-DAC, so then it's just the steering wheel controls (Joycon) that need to be plugged in via USB.
Not that steering wheel controls would help with MX Player, Kodi, and etc anyway.
Also I'll likely be using an external touchscreen as well and mirror the tablet, which so far has tested to be possible.
Yes, you should be able to remove the battery if you like and power it directly, but likely mine will be dockable like others have done and I can just remove it from my RAM Mount tablet holder as I have USB & HDMI connectors fixed in place to make it simple.
I haven't decided about a more permanent mount, as I'd ideally like to mirror the tablet to the permanent touch display and just hide the tablet.