Hi, I am just thinking of connecting a remote kill switch to 12v battery. It will disconnect the 12v battery from the system by just pressing a button on remote. Pretty useful when parking car overnight (when its idle- not needing charging) or when going on vacation. These relays are used in older ice cars having untraced parasitic loads. The only thing i dont know - will bms or some other circuit board throw an error because 12v is being disconnected from circuit-fooling the system. It works well on ice cars but haven't seen anyone use it in ev. There are plenty of chinese remote kill switch on Amazon -- i liked this. Here's the link-- Amazon.com: GMURA Kill Switch for Car, 12V 180A Remote Battery Disconnect Switch, Car Battery Kill Switch Anti Theft, Automatic Cut/Shut Off Switch for Car Truck RV Boat ATV UTV : Automotive
This will be the likely scenario, in addition the 12V accessory battery will then not receive a scheduled (or timed as in the case of HMG) top up charge.
This seems like a bad idea for an EV. EVs charge the 12 V battery from the high-voltage batteries and I know my MINI Cooper SE definitely reports errors if the 12 V battery can't be recharged. The way to ensure the 12 V battery maintains a charge is to keep the EV high-voltage batteries charged. My owner's manual has guidance for what to do if the car isn't going to be used for a long period, I would consult yours.
I would probably install a second, 12 V battery, with a Zener diode to sustain the second battery charge. Then the relay could be used to bypass the Zener and a second relay to disconnect the primary battery. Management of the relays and monitoring the battery states would be an excellent task for a low power, TI MSP430. Wire OR the microcontroller and relay drives from the two batteries and the problem is solved. Just run an LED to signal the good/bad state of the battery assembly ... in either a simple code or my favorite, Morse Code. Bob Wilson
