In older cars the cig. lighter was always ON, connected through a fuse to the battery.
In newer cars, the cig. lighter (and / or "power port") are not powered when the car is turned off, so it would seem that they go through a relay in addition to the fuse.
For example, a "handheld" GPS, plugged into one of these "switched" 12v "power ports", will ... lose external power when the car is switched off.
Since they are not "connected" to the battery when the car is OFF, they will not work for maintaining the 12v battery charge level.
Also, in the EV, do not expect a heavy 100-amp 12v battery. More likely it will be a much lighter, smaller battery, something like 20 to 30 amp-hours (240 to 360 Wh).
Typically, immediately after driving the car, this EV 12v battery will be "full", but have a very small "load", to keep the RFID-detection electronics alive, if nothing else.
See SOC/GID-Meter and CAN-Do Info
2010 Prius, now for sale
2011 LEAF, sold in 2015
2018 Tesla Model 3
2014 Tesla S, Model 3 in 2019
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle