Driving with 12V disconnected

Anyone ever did this inadvertently or not? I am planning to install an automatic disconnect switch on the 12V to protect it from a full discharge and I do not want to trust the switch to not disconnect while the car is running. I obviously want to be able to keep driving with no disruption or negative consequences if this happens.

John (Britprius) has mentioned in another thread that the inverter/Hybrid system might jack up the voltage in this instance.

I am inclined to experiment but NOT if someone else had already burned their fingers with this. Thanks.

 

OK, with the confidence that the system at least protects itself against a *dead* 12V, if not the 12V battery, I went ahead with the test. Here's the sequence I went thru.

1. Disconnect the negative cable from the terminal.
2. Connect one end of a jumper cable to the negative cable going to body.
3. Connect the other end of the jumper cable to the negative terminal on the battery.
4. The car automatically entered the On mode. The Map DVD loading, do not power off message appeared ( I have the navigation system). Waited for the DVD to load, took about 30 seconds.
5. Turned off the system.
6. Pressed the break pedal.
7. Switched on the car, and entered Ready.

Thus far the above is pretty much how a dead battery situation would be handled by anyone, except that I reconnected the original battery instead of getting a jump.

8. Now disconnected the jumper cable from the negative terminal and set it aside.
9. SGII still reading the 14.3V that it normally does.
10. Put the vehicle in Drive and started driving to the grocery store about 5 miles away.
11. After about 3 or 4 minutes SGII showed 13.5V like it always does after the first few minutes.
12. Switched the A/C on. voltage jumped to 14.3 like it does always.
13. Reached the store, switched A/C off, voltage back down to 13.5V.
14. Switched off the car.
15. Manually locked the drivers side door.

Returned after about 30 minutes of shopping to a *dead* car.

16. Opened driver's side door with the manual key.
17. Manually unlocked the rear drivers door.
18. Unlocked and flipped the back seat.
19. Crawled into the back and for the first time fiddled with the hatch release; found the release and after seeing that it's just not enough release it but that while it's released I have to lift the hatch up with the other hand about a foot or so it doesn't close back again, I got down and opened the hatch fully.
20. Reconnected the jumper cable to the negative terminal.
21. Repeated steps 4 thru 13 to reach back home.

Basically once the car entered Ready, the SGII showed the same voltages that I would expect to see with a 12V connected.

Now that I don't have to worry that the car can be influenced by the absence of the 12V while in Ready mode, I am going to test the auto disconnect switch outside of the car and then install it.

Will report back on a separate thread once I am done installing the switch.

NOTE: The above findings are also useful in the event I run into a shorted or messed-up battery that can NOT be jumped. In which case, based on my above test, I can simply disconnect the 12V (just the negative terminal so the positive is held in place away from the body by the dead battery), get the car jumped and get home/wherever.
Also, another option I might consider is a 12V pack consisting of rechargeable AA cells that I need not worry about being sucked dry by the dead battery before I have a chance to get to the On button. In this case, I will disconnect the 12V (negative cable) and then try the small jump pack.

DISCLAIMER: I did the above test on a 2010 Prius III with the navigation/solar pkg with unknown firmware version in the ECUs and such. I am not responsible for any damage in repeating any of the above steps on your car. Try at your own risk.