-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Update on replacing OEM 12v lead-acid battery with lithium?
- Thread starter Pianewman
- Start date
stopcrazypp
Well-Known Member
Because it's a niche application and you are the first one actually to report a result as bad as your's (even the Ohmmu battery that had lots of problem with errors didn't do as bad as your's)? Did you try to plug in a regular 12V to confirm what it usually draws to make sure there is no other vampire load or it's not trying to do a load test? 20A sounds a lot like about how much the car computer draws, so perhaps it is running the full computer momentarily on 12V battery, although generally it should run it on the PCS.
The main high current draw the 12V battery needs to power are the contactors. One draws a peak of about 100A, two would be 200A. This is a piece of cake for lead acid batteries, but some LiFePO4 would struggle. That may be why Tesla chose a higher voltage lithium ion solution (not LFP) instead for their own lithium low voltage battery.
With the new updates and warning system, most people seem to be getting about 4 years of life out of it. At $85 a pop for the lead acid, lithium might not make a lot of sense for people unless it's very inexpensive.
Tesla absolutely has zero incentive to change their BMS to play with lithium batteries. They are going to optimize it to squeeze as much life out of lead acid, while trying to give an early warning for failures (and keep the car awake in those circumstances). It's up to the people designing the lithium replacement batteries to design their BMS to play nice with Tesla's system (basically fool it into believing it's a lead acid).
Last edited:
This is not correct. The coils of the contactors are the only parts connected to the low-voltage battery - these only consume a few watts. Much higher current (hundreds of amps during acceleration, regenerative braking, and DC fast charging) flows through the contacts of the contactors.
The highest loads on the low-voltage system are the electric power steering system and cabin heater (on models without a heat pump).
Non-heat pump heaters run off HV, not 12V. At least that was the case with the S and X and I can't see any reason to change it. Plus 6kW at 12V would be a 500A load which would far outweigh the capacity of the DC-DC converter.
Being an engineer myself, if I thought about how I would manage energy in system that contained:
a) an enormous 85,000 amp hour battery that operates at very high voltage (400 volts) that has huge capacity and can handle huge currents,
but has the downside of high capacity relatively high power draw components. Because even though the
system is off, the large capacity components would draw a lot of current just to be active to supply a small draw necessary to keep the system alive
in an off state. Note: that this 400volt battery, to be used as a power source for the electronic components in the car, an inverter would be required
(which burns energy) to convert the 400 volts down to 12volts to be usable by standard electronics components.
b) To avoid this constant off state large power waste, I would likely add a small battery that has much lower power waste in low power draw conditions,
that would greatly extend the time the car can last in an off condition. When the car is off, I would monitor the voltage in the small battery, and if
it ever started to get low - I would then temporarily turn on the high power battery to charge up the small battery until it was at a safe level -
and then go back into low power state.
c) Such a system design would allow a parked Tesla to last many weeks or even months without all the batteries going dead -- which
is really good, because when all batteries go dead on a Tesla, because it is completely electronically controlled -- the car
becomes completely bricked and you can't even open a door or the frunk, to try to jump start the car!!!!!! (yes I know if you happen to carry a 12volt battery in your pocket it's possible to open the frunk on a bricked car)
d) So how would I manage the small 12volt battery, given this set of circumstances?? Of course, any sane engineer would ALWAYS use power from
the larger battery, and seek to maintain full charge on the smaller battery, as long as the car was in an "on" condition. For this reason, a sane
engineer WOULD NEVER PULL A LARGE DRAW from the SMALL BATTERY while the LARGE BATTERY IS ACTIVE, instead I would just make sure that
the small battery was fully charged.
As I described above, I have been incredibly surprised by what I saw after plugging in a 50 amp hour lithium battery.
Hmmm, I wonder how this Tesla BMS software treats a Tesla 12 volt lead acid battery?
Because I can guarantee you, if it treated it the same as it's treating the lithium battery, the lead acid battery would be destroyed. BTW, the lithium batteries after being discharged at a 20 amp rate until they are down to 12.5 volts, after which the car refuses to charge the lithium battery, is not damaged at all by this treatment. But, I have to open frunk up and charge the battery up manually using a legacy standard 12volt battery charger, but this doesn't help, because you can read my post above to see what happens in this situation.
WHAT HAPPENS IF YOU INSTALL A TESLA LEAD ACID BATTERY?
I guess I shouldn't be surprised by what happens...
With a Tesla lead acid battery install, I watched it as quickly as I could when rebooting the car, I can NEVER SEE IT use any power out of the small battery!!!!!
No matter what situation you but the car in driving, plugged in, not plugged in, I could never catch the car USING power from the 12 volt battery. All I saw was the car putting a gentle 3 amp charging current in to the battery!!!!!
It sure looks like when they detect a Tesla 12v lead acid battery, they treat the battery exactly as I described above, that is VERY GENTLY, and ONLY when the car is OFF.
WHAT COULD THIS POSSIBLY IMPLY?
Given the radically different behavior of the system when a lithum battery is installed NOTHING like how the lead acid battery is treated, and in a way that is so insane that it can only be explained as purposely trying to drain the battery as fast as possible and generate the error condition. I can see no possible way that this is not ON PURPOSE. Because NOTHING about the lead acid behaviour is remotely close to the willful draining and refusal to charge that happens with a lithium battery.
I have put in a service request, which is basically a brief explanation of this problem and a request to fix the Tesla 12volt BMS software to make lithium batteries compatible on the Tesla cars. If you care about this issue, I would ask that as many people as possible bombard Tesla with requests to fix this issue.
Fantastic quality Lithium Iron Phosphate batteries that work out beyond 4000 deep discharge cycles are available at 50 amp hours that are less than half the weight and perform WAY, WAY, WAY better than the Tesla lead acid batties. Wouldn't it be nice to be able NEVER have to face this "replace your 12volt battery" error again?
**** PLEASE JOIN ME IN PRESURING TESLA TO FIX THEIR 12 volt BMS SOFTWARE to to not sabotage lithium batteries!!
a) an enormous 85,000 amp hour battery that operates at very high voltage (400 volts) that has huge capacity and can handle huge currents,
but has the downside of high capacity relatively high power draw components. Because even though the
system is off, the large capacity components would draw a lot of current just to be active to supply a small draw necessary to keep the system alive
in an off state. Note: that this 400volt battery, to be used as a power source for the electronic components in the car, an inverter would be required
(which burns energy) to convert the 400 volts down to 12volts to be usable by standard electronics components.
b) To avoid this constant off state large power waste, I would likely add a small battery that has much lower power waste in low power draw conditions,
that would greatly extend the time the car can last in an off condition. When the car is off, I would monitor the voltage in the small battery, and if
it ever started to get low - I would then temporarily turn on the high power battery to charge up the small battery until it was at a safe level -
and then go back into low power state.
c) Such a system design would allow a parked Tesla to last many weeks or even months without all the batteries going dead -- which
is really good, because when all batteries go dead on a Tesla, because it is completely electronically controlled -- the car
becomes completely bricked and you can't even open a door or the frunk, to try to jump start the car!!!!!! (yes I know if you happen to carry a 12volt battery in your pocket it's possible to open the frunk on a bricked car)
d) So how would I manage the small 12volt battery, given this set of circumstances?? Of course, any sane engineer would ALWAYS use power from
the larger battery, and seek to maintain full charge on the smaller battery, as long as the car was in an "on" condition. For this reason, a sane
engineer WOULD NEVER PULL A LARGE DRAW from the SMALL BATTERY while the LARGE BATTERY IS ACTIVE, instead I would just make sure that
the small battery was fully charged.
As I described above, I have been incredibly surprised by what I saw after plugging in a 50 amp hour lithium battery.
Hmmm, I wonder how this Tesla BMS software treats a Tesla 12 volt lead acid battery?
Because I can guarantee you, if it treated it the same as it's treating the lithium battery, the lead acid battery would be destroyed. BTW, the lithium batteries after being discharged at a 20 amp rate until they are down to 12.5 volts, after which the car refuses to charge the lithium battery, is not damaged at all by this treatment. But, I have to open frunk up and charge the battery up manually using a legacy standard 12volt battery charger, but this doesn't help, because you can read my post above to see what happens in this situation.
WHAT HAPPENS IF YOU INSTALL A TESLA LEAD ACID BATTERY?
I guess I shouldn't be surprised by what happens...
With a Tesla lead acid battery install, I watched it as quickly as I could when rebooting the car, I can NEVER SEE IT use any power out of the small battery!!!!!
No matter what situation you but the car in driving, plugged in, not plugged in, I could never catch the car USING power from the 12 volt battery. All I saw was the car putting a gentle 3 amp charging current in to the battery!!!!!
It sure looks like when they detect a Tesla 12v lead acid battery, they treat the battery exactly as I described above, that is VERY GENTLY, and ONLY when the car is OFF.
WHAT COULD THIS POSSIBLY IMPLY?
Given the radically different behavior of the system when a lithum battery is installed NOTHING like how the lead acid battery is treated, and in a way that is so insane that it can only be explained as purposely trying to drain the battery as fast as possible and generate the error condition. I can see no possible way that this is not ON PURPOSE. Because NOTHING about the lead acid behaviour is remotely close to the willful draining and refusal to charge that happens with a lithium battery.
I have put in a service request, which is basically a brief explanation of this problem and a request to fix the Tesla 12volt BMS software to make lithium batteries compatible on the Tesla cars. If you care about this issue, I would ask that as many people as possible bombard Tesla with requests to fix this issue.
Fantastic quality Lithium Iron Phosphate batteries that work out beyond 4000 deep discharge cycles are available at 50 amp hours that are less than half the weight and perform WAY, WAY, WAY better than the Tesla lead acid batties. Wouldn't it be nice to be able NEVER have to face this "replace your 12volt battery" error again?
**** PLEASE JOIN ME IN PRESURING TESLA TO FIX THEIR 12 volt BMS SOFTWARE to to not sabotage lithium batteries!!
If you live in a cold climate, two years is about what you get out of a lead acid battery (roughly speaking).
Yes, great idea to plug in a 12 volt battery!! See my lengthy post about what happens in this case. Quick summary: absolutely nothing close to what it does with a lithium battery. BTW, the lithium battery I bought cost $120 and if the specs are correct, I should never have to replace a 12volt battery again - which is a pain in the ass and potentially dangerous situation if you are unlucky like I was and have this happen when you're out in the middle of mountains with no power and no cell coverage!!
In observing what happens with a 12 volt lead acid battery in a Tesla while it is powered on, I could NEVER see it actually using any power from the 12 volt battery. The only thing it does is try to charge it at a gentle 3 amps. What happens with a LITHIUM 12 volt battery is willful destruction - 20 amp continuous draw EVEN WHEN PLUGGED INTO A CHARGER until it gets down to 12.5 volts, at which point the error message is generated and the car refuses that charge the 12v battery - even though it is a brand new battery and chargers completely fine with a legacy 12 volt car charger.
stopcrazypp
Well-Known Member
No, I'm talking only about the peak momentary coil switching current. The peak current actually going through the connection is way more than 100A (it's more like 1000A).
Reference to here:
"I just looked up the momentary amp draw of the battery contactor in a Tesla - it's between 100 and 134 amps. I believe there might be two of them, so if they both trigger at the same time, that would be a maximum of 268 amps."
12v Battery Replacement - Latest Recommendations?
From what I can find, on the continuous coil draw of the Model 3 specifically:
"Model 3 contactor 12v amperage pull measured at 8.3A continuous (without economizer)." That's 100W continuous, way more than a few watts. The instantaneous momentary peak draw is probably much higher.
Tesla Model 3 Contactors - openinverter.org wiki
Both of those loads are powered by the PCS (while HV is connected) and not the 12V battery (as others pointed out, cabin PTC heater doesn't run on 12V, but rather high voltage). They also are not on while the car is asleep, so would not contribute to drawing down the 12V battery, while instead the contactors obviously need to be run off the 12V battery when car is asleep (and HV is not connected yet).
OK, with I've learned so far, if I wanted to sue Tesla in a court of law for anti-consumer behavior, I'm sure I would win the case. Here's why I can prove they are actively sabotaging Lithium batteries:
After being forced to replace my brand new lithium battery with a Tesla Lead Acid battery this morning, I was able to observe how the Tesla manages the Lead Acid battery. When I installed the new lead acid battery this morning, it started out at the same voltage as the lithium battery, out of the box at about 12.8 volts. When I rebooted the Tesla with the fresh battery, the battery started increasing in voltage from 12.8 to around 14.5 volts relatively quickly. At around 14.5 volts it kept charging most of day at 6 amps until later in the afternoon when the battery finally reached full charge after about 6 hours charging at 3 amps around 14.5 volts. Once the lead acid battery was fully charged it started trickle charging where it was not charging at all most of the time and periodically it pulsed the battery with one amp for about one second.
After seeing the way the Lead acid behaved when nearly fully charged, I realized the game that Tesla is playing to sabotage the Lithium batteries. Here's the game:
The new lithium batteries on the market today are remarkably compatible with legacy cars and 12 volt chargers. I've installed Lithium on multiple cars up to 20 years old and they worked flawlessly. I've charged the lithium batteries with multiple legacy battery chargers and they fully charge the battery with no issues. Given how compatible these modern lithium batteries are with legacy equipment, why do they not work well with a Tesla?
The answer is: because Tesla has some clever software that detects the difference between a lead acid battery and lithium battery by the way the battery behaves when it is very close to fully charged.
- a lead acid battery has a very FLAT voltage curve when it is nearly fully charged. This means the lead acid stays very near 14.5 volts for many hours when close to fully charged.
- a lithium battery as a very STEEP voltage curve when it is nearly fully charged. This lithium battery spends most of its time timing slowly increasing in voltage from 12.8 volts to 13.8 volts. When it reaches 13.8 volts it very rapidly changes voltage up to 14.7 or 14.8 volts very rapidly.
This is why when I described the behavior of the Tesla BMS when I first watch it fully charge the Lithium battery, I saw this cycle many times:
- keep charging until it reaches 14.6 volts.
- When it reaches 14.6 volts stop charging, and hit the battery with a 17 amp load for a couple seconds.
- ***** by observing the voltage of the battery after hitting it with the brief large load you can DIFFERENTIATE lead acid from lithium with following rule:
** if the voltage is below 14 volts it's a lithium battery
** if the voltage is near 14.5 volts it's a lead acid battery
- it then repeats this cycle several times to make sure it is consistent.
If this quick test determines the battery is lithium, Tesla turns on "sabotage lithium" mode. In this mode, no matter if you are driving or idle or idle and plugged into the charger -- the car will on purpose place a constant 20 amp load on the battery to knock the battery below the 12.6 volts which is the limit below which the "12 volt battery must be replaced" error shows up. My 50 amp hour lithium battery takes a full 2.5 hours at 20 amps to drop below 12.6 volts. In "sabotage lithium" mode it will never again try to charge the battery above 12.6 volts to make the error go away. Once the car is in this mode, the only way to get the voltage up is to disconnect the battery, hook up an external 12 volt battery charger to the battery, charge it up and then reboot the car. Doing this only fixes the problem for a few hours, because once the Tesla fully charges the battery it detects that it's lithium again, and repeats the sabotage.
Now that I've seen this all play out, I am 100% sure that the lithium battery, if it was just managed EXACTLY THE SAME AS THE LEAD ACID BATTERY ***would work perfectly**** This shouldn't surprise anyone, because these batteries work completely fine in every non-Tesla car I've tried them on, and work perfectly with every legacy charger I've tried.
CASE CLOSED **** TESLA BUSTED **** TESLA IS BEHAVING IN AN ANTI-CONSUMER WAY BY DELIBERATELY SABOTAGING LITHIUM BATTERIES *********
I guess this makes sense financially for Tesla. Even though it only takes about 5 minutes to pull out the old battery and plug in a new one and requires only one tool - a 10 mm deep socket - the vast majority of people don't want to bother with this and prefer to pay Tesla $250 dollars to come replace the battery for them. I'm guessing there's 3 million Teslas on the road these days and if the average battery life is 3 years, that means one million battery replacements a year worth $250 million in revenue. So why not screw over the buyers? RIGHT???
After being forced to replace my brand new lithium battery with a Tesla Lead Acid battery this morning, I was able to observe how the Tesla manages the Lead Acid battery. When I installed the new lead acid battery this morning, it started out at the same voltage as the lithium battery, out of the box at about 12.8 volts. When I rebooted the Tesla with the fresh battery, the battery started increasing in voltage from 12.8 to around 14.5 volts relatively quickly. At around 14.5 volts it kept charging most of day at 6 amps until later in the afternoon when the battery finally reached full charge after about 6 hours charging at 3 amps around 14.5 volts. Once the lead acid battery was fully charged it started trickle charging where it was not charging at all most of the time and periodically it pulsed the battery with one amp for about one second.
After seeing the way the Lead acid behaved when nearly fully charged, I realized the game that Tesla is playing to sabotage the Lithium batteries. Here's the game:
The new lithium batteries on the market today are remarkably compatible with legacy cars and 12 volt chargers. I've installed Lithium on multiple cars up to 20 years old and they worked flawlessly. I've charged the lithium batteries with multiple legacy battery chargers and they fully charge the battery with no issues. Given how compatible these modern lithium batteries are with legacy equipment, why do they not work well with a Tesla?
The answer is: because Tesla has some clever software that detects the difference between a lead acid battery and lithium battery by the way the battery behaves when it is very close to fully charged.
- a lead acid battery has a very FLAT voltage curve when it is nearly fully charged. This means the lead acid stays very near 14.5 volts for many hours when close to fully charged.
- a lithium battery as a very STEEP voltage curve when it is nearly fully charged. This lithium battery spends most of its time timing slowly increasing in voltage from 12.8 volts to 13.8 volts. When it reaches 13.8 volts it very rapidly changes voltage up to 14.7 or 14.8 volts very rapidly.
This is why when I described the behavior of the Tesla BMS when I first watch it fully charge the Lithium battery, I saw this cycle many times:
- keep charging until it reaches 14.6 volts.
- When it reaches 14.6 volts stop charging, and hit the battery with a 17 amp load for a couple seconds.
- ***** by observing the voltage of the battery after hitting it with the brief large load you can DIFFERENTIATE lead acid from lithium with following rule:
** if the voltage is below 14 volts it's a lithium battery
** if the voltage is near 14.5 volts it's a lead acid battery
- it then repeats this cycle several times to make sure it is consistent.
If this quick test determines the battery is lithium, Tesla turns on "sabotage lithium" mode. In this mode, no matter if you are driving or idle or idle and plugged into the charger -- the car will on purpose place a constant 20 amp load on the battery to knock the battery below the 12.6 volts which is the limit below which the "12 volt battery must be replaced" error shows up. My 50 amp hour lithium battery takes a full 2.5 hours at 20 amps to drop below 12.6 volts. In "sabotage lithium" mode it will never again try to charge the battery above 12.6 volts to make the error go away. Once the car is in this mode, the only way to get the voltage up is to disconnect the battery, hook up an external 12 volt battery charger to the battery, charge it up and then reboot the car. Doing this only fixes the problem for a few hours, because once the Tesla fully charges the battery it detects that it's lithium again, and repeats the sabotage.
Now that I've seen this all play out, I am 100% sure that the lithium battery, if it was just managed EXACTLY THE SAME AS THE LEAD ACID BATTERY ***would work perfectly**** This shouldn't surprise anyone, because these batteries work completely fine in every non-Tesla car I've tried them on, and work perfectly with every legacy charger I've tried.
CASE CLOSED **** TESLA BUSTED **** TESLA IS BEHAVING IN AN ANTI-CONSUMER WAY BY DELIBERATELY SABOTAGING LITHIUM BATTERIES *********
I guess this makes sense financially for Tesla. Even though it only takes about 5 minutes to pull out the old battery and plug in a new one and requires only one tool - a 10 mm deep socket - the vast majority of people don't want to bother with this and prefer to pay Tesla $250 dollars to come replace the battery for them. I'm guessing there's 3 million Teslas on the road these days and if the average battery life is 3 years, that means one million battery replacements a year worth $250 million in revenue. So why not screw over the buyers? RIGHT???
stopcrazypp
Well-Known Member
That $120 price makes me suspect the issue is the BMS in that lithium battery or there is something iffy about it.
The Ohmmu battery that most people have used (and still got problems) instead is $480.
12V Lithium Battery for TESLA Model 3
From the other threads, even the problematic ones can last a week or two before popping an error, not pop the error almost immediately in hours like yours did.
Looking more closely at your original post, you report the 20A draw after it pops the error. Actually when a Tesla pops the error, it never goes to sleep again, so the HV is always connected. That means it should be drawing from the PCS now. It also should stop using or charging the 12V given it has determined it's a failed battery. This mode was added after people have gotten stranded and this have helped many people be able to have a failed battery and still use the car while they get it replaced.
Where are you seeing this "20A" number? Are you certainly it doesn't include draw from the PCS? 20A is on the order of how much the car should be drawing while it's awake to keep the computers on.
Last edited:
Last edited:
From what I've uncovered the last few days, if the Ohmmu is a lithium ion battery, it would have the same issue as the one I have. The only way to avoid this problem would be if you had some fairly complex electronics that have to be able to maintain 14.6 volts being drawn at 17 amps for a couple seconds. I think a pretty hefty capacitor might be able to do the trick, but I really have no idea because I've never touched an Ohmmu.
If that's what I said, about the 20A draw only happening AFTER it pops the error, that was written incorrectly. The 20A draw starts happening right fairly soon after the routine to determine it's lithium runs. The first time this happened I was driving so I could not monitor what and when it happened. The second time I tried it my car was sitting in my garage while plugged in and I could see the 20A draw in a fairly short amount of time way before the error message shows up. The error message only shows up a fair amount of time after the 20A draw down has dragged the voltage down far enough.
Yes, once the error happens the car will never sleep, nor will it charge the battery up above 12.6 volts again. NOTE: if you reboot the process with a lithium battery you that is new of you have manually charged to at least 12.8 volts, the Tesla will charge that lithium battery all the way up to 14.6 volts. But it only does this once, because once it's at 14.6 volts and runs the "battery type detection routine" it will only drain the voltage to below 12.6 volts and never charge it again. To me this is proof of deliberate sabotage. If it could charge it up once, why couldn't it charge it up again? Also, what happens with a lead acid bears NO resemblance to what the Tesla does to a Lithium battery.
I think California prices are higher than what you are showing. But in any case thats's still $129 million dollars a year revenue for Tesla.
Just copied from evseekers.com:
Tesla 12v Battery Replacement Cost (Revised Estimate)
Even though Tesla does not fully publish the estimated cost to the public, most users have reported paying between $120 and $250 for the Tesla Mobile Service. Some even claimed to have paid up to $70 in extra labor costs for the service.
Replacing the 12v Lead Acid battery of Tesla older Models may cost between $150 and $500 via Mobile mechanic service including labor expenses 30 to 50.
So it looks like you're pretty lucky if you only paid $129.
stopcrazypp
Well-Known Member
You say it's a lithium detection routine, but it's more likely just the standard failing lead acid detection routine. This routine used to not exist and there were people stranded. So Tesla added a routine to detect a lead acid battery that is failing and this is the result. There aren't very good ways to detect lead acid that is on the way out, other than a load test, and this may be what it is after it detects the battery is behaving in an unexpected way (which a lithium battery is prone to do). Basically what Tesla is trying to avoid is the battery suddenly dying without warning and the car won't have time to keep the car awake.
ICE cars are different given typically you get some clue the battery is on the way out on how much effort is needed to provide the hundreds of amps, although from other threads, actually there are still plenty of people that have the battery die on them with no warning.
stopcrazypp
Well-Known Member
$85 seems to be the price everywhere including in California. Most of them are replaced under warranty, so Tesla isn't getting real profit from it (it doesn't cost Tesla $0 for the battery or labor). $85 is a very good price for a sealed battery of this size. I think people have looked and there aren't any third party ones that come close.
As for labor in California, here's someone that got it replaced in California at their own driveway, it was ~$120 total, $85 for the battery, the rest being labor and taxes:
Poll: How many are still using original 12V Battery that came with the car?
Similar threads
