Battery Leak

Diehard

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I have read some conflicting info and need some clarification. I understand BEVs lose charge just by sitting there. That is mostly due to the car doing it's own thing with battery maintenance, spying and other duties but aside from that my understanding is that even if battery is disconnected, it could lose 3%-10% in a month. Is that understanding correct? If it is, is that loss inversely proportional to state of charge? In other words is a CT parked at 90% SOC is leaking faster than one at 50% SOC? Drop some knowledge on me if you have it please.

 

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What I've seen from others (don't have an EV yet):
  1. Sentry mode is a huge drain. Might want to charge up if you're going to leave the car for even a few days. Or, better, have it parked and connected in a charging location.
  2. Car parked, but with Sentry mode disengaged you lose perhaps a few % per day, depending on whether you also have it set to maintain cabin temperatures (e.g. don't exceed 120°F / 49°C)
  3. Car completely off results in almost no drop in SoC even over a couple of weeks. Maybe 1-2%.
Would love to hear owners' experiences in this thread. This is just the semi-understanding I've gleaned from the YouTubes and Twitters.
 

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The principal culprit has been AGM 12v Tesla uses to keep non-battery pack essentials energized while the battery pack is at rest. That little 12v battery drains dead, that Tesla gets a flatbed ride back to Tesla for a cold boot reinstantiation of its electricals.

Tesla announced AGM is superceded by SS 12v battery. No news how that changes battery drain.
 

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In my experience of living a week unplugged with my Model Y, I lost about 2% per day.

Now that’s not “Powered down”, I was sleeping in it, but even when I wasn’t using camp mode, it was still firing up the computer and doing things which required the car be “woken up”. I did have Setry Mode and most other automatic features disabled, but needed to get in and out of the car so it was awake at least part time.

I’m sure it would do a lot better without me piling in and out 3-4 times a day, but it still uses some power.

Starting to think every EV should ship with at least a small solar panel to keep the car‘s 12v system healthy and keep basic functions going without tapping into the reserves.

Side note… it’s not going to be 12v for long, Musk has been rumbling about switching to 48v and marrying communications and power delivery. I think they are likely to roll something similar to Power over Ethernet for the whole car.
 
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Diehard

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Side note… it’s not going to be 12v for long, Musk has been rumbling about switching to 48v and marrying communications and power delivery. I think they are likely to roll something similar to Power over Ethernet for the whole car.
Does that have any impact on power consumption when it is not moving?

I guess it means if the 48V battery dies, I can't wake it up getting a jump from an ICE.

That little 12v battery drains dead, that Tesla gets a flatbed ride back to Tesla for a cold boot reinstantiation of its electricals.
There are a ton of youtube videos of people bringing their Tesla back to like with a 12V jump box. Some Tesla's are different than others or there are different levels of dead?

This guy didn't seem to need Tesla to replace his battery:
 
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Does that have any impact on power consumption when it is not moving?

I guess it means if the 48V battery dies, I can't wake it up getting a jump from an ICE.
Seems unlikely an ICE jump will help.

It should be a little more reliable and save a bunch of weight. It takes fat wires to push power around at 12v, at 48v you just need 1 twisted pair on Ethernet (maybe something industry specific but similar).
 

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There are several functions of the 12V, and there were recently pictures from China built Model Y’s with a new integrated lithium 12V battery into the vehicle.

I may not be understanding your question fully, but if you leave your CT unplugged, you will have what most refer to as “vampire drain”. This will be from cabin overheat protection, sentry mode, basic battery chemistry and retention principles that are way over my head to explain, and having your vehicle on standby.

These all reduce the available state of charge available to you at about 1% per day, and could be more depending on the activation of these other features.

Jumping the 12V won’t get you anywhere, but will allow you to access your vehicle, as the locks are tied to the 12V.

I haven’t seenState of Charge drop more rapidly if it’s starting at one % over another.

For those without experience with an EV yet, you really do adjust to all these little nuances that may seem concerning up front. It’s a slightly different car ownership lifestyle, but in the end, it’s far better than my experiences with ICE vehicles
 

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One other comment on this.

After the car gets below 20% charge, many of these features get disabled automatically. Sentry mode, summon mode, and cabin overheat protection all shut off when battery if below 20%.
 

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Hi all
I think solar cells being inbuilt into the vehicle is a great idea, i will definitely be getting the solar cell upgrade on my cybertruck before anything else.
It might hopefully give us about ten miles of free traveling a day to. They will be specially good for camping and running all of those accessories.
Have a good day all.
 

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Also…

Vampiric drain on the Cybertruck will be less than on other vehicles because it has a bigger battery. Many of the things which cause drain burn a set amount of power so the bigger battery will power those things for longer. Even cabin temp regulation won’t take as much power relative to the battery size.
 


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Diehard

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I may not be understanding your question fully, ....

Jumping the 12V won’t get you anywhere, but will allow you to access your vehicle, as the locks are tied to the 12V.

I haven’t seenState of Charge drop more rapidly if it’s starting at one % over another.

My question came from an article I read that suggested all Lithium-ion batteries self-discharge. That lead to two thoughts/concerns:

1 - If I had to leave the car for extended period unplugged and turned off / disconnected everything I could, how long would it take before the pack go to zero and get damaged. This is mostly a thought exercise. If I have to leave it at home for extended time, I could keep it plugged in.

2 - I was trying to see if there is any best practices to reduce that self discharge loss, not the Vampire loss everyone has been explaining which is due to consumption. However it seems like it is a much smaller loss than vampire loss. And because it is smaller, I doubt it could be noticed as easily with a connected pack while the car is operational. I am still curious if that loss is faster at higher SOC or it is linear.

From everyone's response, I have gotten a good sense of how much I can play with before things get critical with SOC and it seems like self discharge rate is too low to peak anyone's interest except the geekiest of the geeks among the members.

I also have read several posts from Tesla owners claiming they have jump started their cars. Apparently once 12V battery closes the contactors and 12V DC-to-DC converter start the car (wakes it up), car can move without 12V battery's help until the next time it needs to wake up (assuming the main pack is not dead).
 

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Sentry mode is the biggest parasitic power hog in my Mod3. I have learned to leave it turned off by default and use it only when necessary (I.e, parking in an unfamiliar area). When not using that I notice virtually no parked power consumption.
 

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My question came from an article I read that suggested all Lithium-ion batteries self-discharge. That lead to two thoughts/concerns:

1 - If I had to leave the car for extended period unplugged and turned off / disconnected everything I could, how long would it take before the pack go to zero and get damaged. This is mostly a thought exercise. If I have to leave it at home for extended time, I could keep it plugged in.
A Tesla cannot be fully powered down. It needs at least a small amount of power to keep the RFID scanner active for the key card. I’m sure there is some small drain as you suggest, but there is always at least a small load on it to guarantee it will drain.

It’s likely a 50% state of charge is idea for long term storage but that’s a bit of a wag.

I’m picturing in the distant future someone stumbling across a barn filled with dead Teslas covered in dust now.
 

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My question came from an article I read that suggested all Lithium-ion batteries self-discharge. That lead to two thoughts/concerns:

1 - If I had to leave the car for extended period unplugged and turned off / disconnected everything I could, how long would it take before the pack go to zero and get damaged. This is mostly a thought exercise. If I have to leave it at home for extended time, I could keep it plugged in.

2 - I was trying to see if there is any best practices to reduce that self discharge loss, not the Vampire loss everyone has been explaining which is due to consumption. However it seems like it is a much smaller loss than vampire loss. And because it is smaller, I doubt it could be noticed as easily with a connected pack while the car is operational. I am still curious if that loss is faster at higher SOC or it is linear.

From everyone's response, I have gotten a good sense of how much I can play with before things get critical with SOC and it seems like self discharge rate is too low to peak anyone's interest except the geekiest of the geeks among the members.

I also have read several posts from Tesla owners claiming they have jump started their cars. Apparently once 12V battery closes the contactors and 12V DC-to-DC converter start the car (wakes it up), car can move without 12V battery's help until the next time it needs to wake up (assuming the main pack is not dead).
Some info for you about the high voltage battery pack (and also about the 12v battery because some people here have bad info).

The high voltage lithium ion battery is not always "connected" in a Tesla. When the car goes to sleep (that is after you park the car and leave it for 15 minutes) the high voltage battery contactors disconnect. Those contactors are basically relays. The car's computer still uses some power to be able to detect one of the multiple types of keys getting near or being placed near the B-pillar scanner, as well as listening for any queries or commands from the Tesla servers that originate from the owner's Tesla app. There are a lot of other monitoring functions and they all run on the 12v battery. When the computer determines that the 12v battery should be recharged, it will close the high voltage contactors and charge it via the DC to DC converter. The DC to DC converter is like an alternator and converts from the high voltage of the battery pack to the low voltage of the 12v system. The only 3 components in the car that run directly off of high voltage are the drive motor/s, AC compressor, and cabin heater (AC compressor and cabin heater are one item in newer Teslas that have a heat pump).

"Phantom drain" is the energy used up by the car when you are not driving it. It includes the processes mentioned above as well as Sentry Mode (optional feature), Cabin Overheat Protection (optional feature), battery conditioning (done automatically to keep the battery pack temps within safe limits for longevity).

As to your question of any drain on the battery pack if you disconnected it from everything, it might be around 3% per month due to the internal self discharge, which all batteries of all chemistries suffer from (at different rates). Lead acid batteries discharge at 2x that rate (https://en.wikipedia.org/wiki/Self-discharge). If the Tesla high voltage battery pack gets very low (not sure of the exact cutoff), it will not charge the 12v battery anymore and not engage the HV contactors to protect itself. It would mean that eventually the 12v battery would die and you would have to jump start the 12v battery or replace it to get the car working again. Yes, you can jump start the 12v battery and 12v system in the car just like with any other car. You can also replace your own 12v battery and you can buy it at any auto parts store.

Here's something else to keep in mind: you don't ever want to store a lithium ion battery at a high state of charge because it causes a little bit of irreversible damage that over time leads to some capacity loss. Also, on Model 3, Tesla balances the battery cells if the charge level is above 85%. This might cause a slightly higher loss of charge if stored above that level as the BMS (battery management system) uses small resistors to bleed off power from the higher voltage cells in order to match the lower voltage ones. This should be a very tiny amount and probably not even worth thinking about.
 
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Diehard

Diehard

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you don't ever want to store a lithium ion battery at a high state of charge because it causes a little bit of irreversible damage that over time leads to some capacity loss.
I really appreciate the super helpful info shared in quite digestible fashion. That brings another question: This probably wouldn't apply to CT but on current Teslas, would replacing the 12V battery with a lithium ion battery require any software adjustment so that main pack does not over charge it? or these batteries are responsible to protect themselves with their own circuits? and simply replacing the old battery with 12V lithium ion is safe?

 

 
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