In the process of making this, I learned some things about how Tesla manages the 12V battery charge state. At this point, it appears that the vehicle may not charge the 12V battery if the main battery level falls to 44%. I'd have to do some further testing to try observing what the 12V battery voltage does when the vehicle is driven and the main battery is below 50%.
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12V Battery Health Check
- Thread starter Padelford
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- 12v battery health Model X
In the process of making this, I learned some things about how Tesla manages the 12V battery charge state. At this point, it appears that the vehicle may not charge the 12V battery if the main battery level falls to 44%. I'd have to do some further testing to try observing what the 12V battery voltage does when the vehicle is driven and the main battery is below 50%.
Yes, I directly observed this when the vehicle is at rest. I can’t comment on what happens when the vehicle is being driven. I would either have to rig up a remote voltmeter, or perhaps Scan My Tesla shows the 12V battery voltage.
As I recall, others have commented that running down the main battery puts stress on the 12V battery. If the vehicle stops keeping the 12V battery charged when the main battery runs low, the situation would be like an ICE with a bad alternator.
mbp11
Member
Thanks for the video, this was usefly. I was not sure where the positive lead was in the frunk, I though we had to tear out the frunk tub to get to the leads of the battery to test it. Should there not be some kind of cover over the hot lead, something bright red, to keep people who are inquisitive from accidently touching it and grounding the battery out? I am certainly going to try to find something form my X that will keep it covered, even in the fusebox, to keep idiots like me from getting close.
Anybody know what to look for in terms of figuring out the health of 12V battery? Getting a ton of phantom drain so wondering if my 12V is about to go but no message/warning from Tesla yet.
what statistics do I need to look for? I gather a simple voltage check won’t cut it. Will one is those digital battery analyzer that measure cranking amps do the trick?
what statistics do I need to look for? I gather a simple voltage check won’t cut it. Will one is those digital battery analyzer that measure cranking amps do the trick?
mspohr
Well-Known Member
My nosecone S has a red plastic cover over the + terminal behind the nosecone. Don't know what other models do.
mbp11
Member
I have a July 2018 Modex X 100D, and mine came without anything on top of the hot lead. I found a red cap and taped it on for safety.
see my video above. With the vehicle off overnight, check the battery terminal in the frunk fuse box for voltage to ground. Don’t activate the vehicle. If the battery voltage reads below 12.4 VDC, the battery is questionable, and if < 12 V it should be replaced.
Watts_Up
Well-Known Member
I have a Model 3 but I assume this would be applicable for your Model X.
About the 12 V battery, the first concern I have would be to be able to check if the car is asleep when the car is locked.
I always noticed after a new software update that some people complained that their car would no go back to sleep mode.
In the case of the Model 3, beside the noticeable 'Dong' noise every time the car goes to sleep or weak up,
there is no real way to know if the car is asleep.
I put on top of my console, a little wireless charger connected to the auxiliary 12 V plug.
The wireless charger has a red LED when connected, which turns blue when charging a phone,
and the LED is off when there is no power.
So from the outside I can see if the car 12v auxiliary power is on or off.
Also if I choose to keep the Sentry on, the red LED stays on, which is a simple way to check the Sentry status.
there is no real way to know if the car is asleep.
I put on top of my console, a little wireless charger connected to the auxiliary 12 V plug.
The wireless charger has a red LED when connected, which turns blue when charging a phone,
and the LED is off when there is no power.
So from the outside I can see if the car 12v auxiliary power is on or off.
Also if I choose to keep the Sentry on, the red LED stays on, which is a simple way to check the Sentry status.
Anyway I would recommend installing a 12 V battery monitor which can be access remotely using a Bluetooth app from your phone.
The app displays a continuous voltage voltage of the battery.
Typically if you are not driving, the 12 V battery slowly get discharge and when reaching about 12.50 V
(after 2 days in my personal case) the inboard charger get activated and charge the 12 V battery at 14 V during 2 hours.
At the end of charging, the battery returns to a steady 13 V and starts again slowly discharging until reaching 12.50 V.
This could be a good way to determine if there is any thing wrong with the 12 V battery
and in particular if the battery cannot keep the charge and need to be constantly recharged,
this could be an indication that the battery needs to be replaced.
(after 2 days in my personal case) the inboard charger get activated and charge the 12 V battery at 14 V during 2 hours.
At the end of charging, the battery returns to a steady 13 V and starts again slowly discharging until reaching 12.50 V.
This could be a good way to determine if there is any thing wrong with the 12 V battery
and in particular if the battery cannot keep the charge and need to be constantly recharged,
this could be an indication that the battery needs to be replaced.
About statistics results, from the above graph, the battery loses about 0.50 V every 2 days, or 50 hours, so about 10 mV per hour.
If later on you notice a faster voltage decrease than what you observed, this could be an indication of battery degradation.
However, some time the duration between recharge varies, like one day and a half to three days.
I think the cause was some climate temperature variations at night principally as I noticed the pumps
keeping the propulsion warm running more continually.
Honestly from @Padelford above observation in the video, I never tested if the internal charger would stop recharging
the 12 V battery when the SoC of the propulsion battery is below 40% or any other number.
I'll eventually try to check this hypothesis.
I think the cause was some climate temperature variations at night principally as I noticed the pumps
keeping the propulsion warm running more continually.
Honestly from @Padelford above observation in the video, I never tested if the internal charger would stop recharging
the 12 V battery when the SoC of the propulsion battery is below 40% or any other number.
I'll eventually try to check this hypothesis.
Another way to test the 12 V battery status would be to discharge the battery using an external load,
allowing to monitor both the Voltage and the Amp to determine the internal resistivity of the battery.
I noticed that when Sentry is activated, the battery jump to a steady 13.40 V so I guess the DC/DC charger is running.
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mbp11
Member
I have a followup question of the collective wisdom. I have used the tools provided on this forum and You Tube to resuscitate several Teslas, and I just did a Model S today that had completely dead 12 volt and high voltage battery (owner went to India, thought he would get back in 2 weeks but was stuck there for 6 weeks). Now the question comes in.... We got the Tesla running and got the charge port open and the car is charging.... how long can I safely leave the battery charger attached to charge the 12 volt battery while the car is at Zero charge right now? Should I wait until the car is 10% charged before disconnecting, 20%, what? It will take time for the 12 volt battery to charge while the car is at zero.
Mike Peterson
Pleasanton CA
Mike Peterson
Pleasanton CA
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