12V battery reads 7V -- Traction Battery Fine -- Leaf won't start.

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brycenesbitt

Well-known member
Joined
Jan 31, 2016
Messages
151
So we left the Leaf for a week. On return the doors would open, but the horn was weak, pressing the emergency flashers caused the dome light to flash also, and it would not charge. The car would not turn on fully, battery capacity showed as "---".

I recharged the 12V battery manually, and the thing sprang back to life. The traction battery instantly shows at about 70%.

What could have happened? I thought the 12V battery would get charged from the traction battery? Why would a low 12V battery cause a failure to charge?
 
There are many threads on this, but the short version is: if you left the car plugged in but not charging (not likely here) that alone will kill the accessory battery. If you left a bluetooth dongle for LeafSpy plugged in, that too can kill the battery. If neither of those, then you have a phantom load on the car's 12 volt system when it is off.
 
Or the 12v battery is bad :)
The OP didn't say how old it was, but if over 3-4 years it's probably bad.
 
Op here.
It's a 2011 Leaf with solar panel for the 12V system, and a LELink Bluetooth OBD II adapter for Leaf Spy, always plugged in.

Symptom: Leaf won't start, horn weak, dash lights up but range shows "---", and all dash lights are on, the car just acts like the engine computer is dead. It won't accept a charge either. Everything is inconsistent and it changes from moment to moment. For example the car says the parking brake is on, but won't recognize releasing the parking brake.

Observation: 12V battery reads about 7 Volts.

Short fix: Charge the 12V battery with an external charger. The car comes back to life, though once I had to pull the ground wire to the battery first. The car forgets how much power is in the traction battery, so it comes up reading 1 mile on the GOM.

Long fix: pending new battery purchase (and maybe a https://www.pulsetech.net/ battery maintainer.
 
LeftieBiker said:
I suggest you also get a Bluetooth dongle that turns off with the car.
Not sure if they have one that "turns off with car" but some BT dongles have a little switch on them, which enable you to manually turn it OFF if you chose. In hind site I kind of wish I had spend the extra $10 or so it would have been for one with a switch but the $12 I got mine for was too tempting and has been working fine for going on 3 years.
 
7 years is a long life span on the original factory 12 volt 2011 LEAF battery. It was bound to fail soon, given the history of other cars on the forum.

Replace the 12 volt battery, and you're good to go for a few more years...
 
Unfortunately the Leaf Spy recommended BT adapter Bluetooth Konnwei KW902 gets terrible reviews and has no on/off power saving features. Honestly I doubt the problem was the BT adapter, it was not in all the time, and the amount of energy used is pretty small compared to the watt hour rating of the 12V battery.
 
brycenesbitt said:
Unfortunately the Leaf Spy recommended BT adapter Bluetooth Konnwei KW902 gets terrible reviews and has no on/off power saving features. Honestly I doubt the problem was the BT adapter, it was not in all the time, and the amount of energy used is pretty small compared to the watt hour rating of the 12V battery.

Still, it can add up over time and actual consumption doesn't always match the seller's claims. Combined with an already-old battery...

A new battery should set things straight. Consider removing the dongle if leaving the vehicle unused for more than a few days. You can also get an OBDII extension cable that gives you the option to turn it off, and also relocate it to a more convenient location.
 
WiFi like mine drains more amps and must be disconnected if idle over a day. I bought an extension cord so I almost never mess with the connection under the steering wheel. I can just disconnect adapter as it sits on console. That connection to vehicle seems very fragile and I understand is very expensive to fix.
 
On 2011 and 2012, automatic 12-volt battery charging while parked is fixed at a few minutes every 5 days. The Bluetooth unit draws a small amount of power and keeps other modules active so it interferes with the automatic charging. You will discharge the 12-volt battery if you leave the dongle plugged in to a 2011 or 2012 during long-term parking. You may get away without draining the 12-volt battery on later models, but I strongly recommend that the dongle be unplugged for extended parking of any LEAF.
 
I was in the garage the other day next to my '12 when all the sudden I heard relays clicking. I looked at the car and saw one of the blue charging lights start flashing(not middle but can't remember what side) but my Leaf wasn't plugged in :? Maybe it was charging the 12v battery?? It lasted about 5 minutes and quit as fast as it started.
I've never heard my '13S do this before, but then again I've not seen the '12 do it either, sounds like one would have to be very lucky to catch it in action.
 
What else might interfere with the 12V charging? Do you have a reference to the exact details of what interferes on the 2011/2012?

GerryAZ said:
On 2011 and 2012, automatic 12-volt battery charging while parked is fixed at a few minutes every 5 days. The Bluetooth unit draws a small amount of power and keeps other modules active so it interferes with the automatic charging.
 
I know from experience that leaving an OBDII Bluetooth unit plugged in will keep enough modules awake to drain the 12-volt battery when parked for more than a couple days on my 2011. I also had a small auxiliary relay that supplies power to the shift control module stick closed on more than one occasion and believe that would have drained the battery if I had not replaced it before extended parking.

The upgraded telematics control unit has drained the battery in the 2015 at least once so I suspect an upgraded TCU in a 2011 could also cause that issue.
 
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