How to find an intermittent phantom 12v load

I (like so many others here) am having nonstop problems with my 12v battery. (Batteries, actually, as the dealer's go-to solution is to just replace it without fixing the underlying problem. ) I've taken it in to the dealership several times and they monitored it but were unable to find any phantom loads on the battery. Right now I have to connect the 12v to a tender/maintainer all night every night, and I still get the EV warning system light each morning (the yellow car with the exclamation point in it--for my car this light is the most reliable indicator of 12v battery issues. The other indicator being that the touch screen is randomly triggered when I'm not touching it).

I've eliminated the obvious possibilities:

• The problem is not related to leaving the car plugged in while not charging.
• The problem is not related to a bad or old battery.
• The problem is not related to an OBDII or leaf spy device. I do have a USB drive plugged in and a USB charger plugged into the cigarette lighter.

I currently suspect the TCU unit, but I'm not sure how to catch it in the act. Is there some sort of smart voltage meter that I can attach which will log power draw over time? Are there particular TCU events that I can test around?

There are recording multimeters available.

It's remarkable that the battery is draining even with a maintainer attached. That would take a considerable and persistent load. Are you sure the warning light corresponds to a low 12V battery? What voltage are you seeing?

Since you're getting a warning light, getting the codes from LeafSpy could be very useful.

The other thing I'd be looking to verify that the 12V charging system is working. Perhaps it's not a phantom load issue but a charging issue.

Nubo said:

It's remarkable that the battery is draining even with a maintainer attached. That would take a considerable and persistent load.

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It isn't draining when the maintainer is attached--however the battery is badly damaged at this point so I think that is why I'm seeing the EV system warning light. The maintainer is usually charging at 14.x volts and .9ish amps in the morning when I unplug to go to work.

Nubo said:

Are you sure the warning light corresponds to a low 12V battery? What voltage are you seeing?

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Not sure, but every time I've started seeing that light there have been 12V battery problems within a few days. (E.g., car won't start in the morning without a jump.)

Nubo said:

Since you're getting a warning light, getting the codes from LeafSpy could be very useful.

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Will look into it. The OBDII I bought previously didn't work with LeafSpy.

Nubo said:

The other thing I'd be looking to verify that the 12V charging system is working. Perhaps it's not a phantom load issue but a charging issue.

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I think it is working because when the battery was drained completely, I jump started it and left the car on in READY mode for an hour, and after that I was able to turn the car on without problem. Also, the EV system warning light usually turns off after I've driven for a while and turn it back on again without letting the car sit for too long.

I get the EV warning light whenever the telematics unit fails to go into low power (sleep) mode. This causes the other modules in the car to stay active and drains the 12-volt battery over time. Error codes read with LEAF Spy from this include something like "EV System Incomplete Shutdown" which makes sense since the modules are staying active and draining the 12-volt battery. The EV warning light goes off after driving, but will come back unless I disconnect the 12-volt battery or pull the fuse that feeds the telematics unit to reset the telematics module. My deep cycle battery can sustain this load without getting excessively discharged as long as the car is driven every day.

I suggest you get a suitable OBDII adapter and use LEAF Spy Pro to read and reset error codes in addition to disconnecting power to the telematics unit whenever you notice the EV System warning light.