12V battery: convert to a cheap alternative?

[Vercingetorix]

Maybe? But you’re solving for a problem that doesn’t really exist.

Very few cars come with 12v lithium batteries from the factory. Literally hundreds of millions of AGM batteries make it through winter just fine. And they come with a few years of replacement warranty just in case.

FWIW, I don’t know what I will do if my 12v goes out, but it’s good to have options.

In my opinion the AGM battery is solving a problem that doesn’t exist. Discharging the Taycan lithium 12v battery to 50% from 100% EVERY DAY should still net 10 years of life. Discharging 20% a day gives 20+ years. AGM sucks by comparison. I fully expect my Taycan battery to last the life of the car. I would have no issues buying one from a wrecking yard.

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[69Mach390]

In my opinion the AGM battery is solving a problem that doesn’t exist. Discharging the Taycan lithium 12v battery to 50% from 100% EVERY DAY should still net 10 years of life. Discharging 20% a day gives 20+ years. AGM sucks by comparison. I fully expect my Taycan battery to last the life of the car. I would have no issues buying one from a wrecking yard.

I hope mine lasts that long too.

But based on the fact that this car has only existed for 6 years and there are plenty of people who have already replaced the 12v (at about a $3500 out of pocket cost), I would say this is a problem that DOES exist.

 

[gamueller]

I fully expect my Taycan lithium 12v battery to last the life of the car.

Why would we expect the 12V battery to be any better than the 800V battery?

 

[ecko04]

I don’t believe this is a problem that’s specific to Porsche. There’s no question that lithium technology is superior, but I haven’t come across a manufacturer who has switched to lithium for its low voltage system address premature failure, which brings into question whether it’s fit for purpose.

Given the cost of lithium replacements, I’m glad to see an option to move to AGM if needed. I’ve had my lithium show 0.0v but luckily I was able to get the BMS to wake it up by directly connect another 12v battery to the jump points since a typical charger wasn’t doing the trick.

I welcome options.

 

[ct14garage]

Reasons AGM are worse than lithium.

Bullshit, if the Taycan couldn't use AGM batteries, its Gateway wouldn't have a coding option to support it from factory.

If Lithium was so good Porsche factory wouldn't have rolled back to AGM on the 2026 Cayenne / Panamera models.

And to finish it, most cars that we replace their Lithium to AGM are at the 3 years old mark. They don't last the life time of the car like you think, far from it, these cells swell, and not only that but if deeply discharged the BMS will lock and open the relay to protect the Lithium cell and unless you reprogram it the battery is toast. Can't even charge it.

AGM if it deeply discharges you just charge it back and that's it.

Not to mention that AGM LN0 costs $60 whereas 123Systems shit costs over $3,000

Let 123Systems stick their shitty batteries where the sun never shines!

By now over 200 cars converted at my shop from Lithium to AGM within the past 2 and half years. Not a single customer has complained

 

[Dee]

Reasons AGM are worse than lithium.

What is the discharge current? (CCA, cold cranking amps)
It doesn't say anywhere.

That analogy doesn't go for EV batteries as they don't have to feed a big high amps starter motor which are used in ICE cars.
The reason a 12V battery in an EV last a long time is the absence of extreme high cranking power current.
They are half the size of a regular 12V battery of an ICE car, and that's for exactly that reason.

@ct14garage Thanks for explaining.

 

[Dee]

I hope mine lasts that long too.

But based on the fact that this car has only existed for 6 years and there are plenty of people who have already replaced the 12v (at about a $3500 out of pocket cost), I would say this is a problem that DOES exist.

That's cuz it's drained and not charged by the car, that's the real issue, software related.
If it gets below a certain voltage treshold the BMS of the 12V battery is shutting it down, end of battery (for normal people).

If it's charged by the car there are absolutely zero issues with the 12V batteries.
Mine's almost 6 years old, no problem.
It can sit for at least two weeks and it's still being charged by the car so my software is working ok and so does the battery.

 

[ovonrein]

most cars that we replace their Lithium to AGM are at the 3 years old mark.

That statement baffles me. What makes these Lithium batteries fail after only 3 years?

 

[prj]

That statement baffles me. What makes these Lithium batteries fail after only 3 years?

Cell defects. Super widespread on the Cayenne as well.

 

[ct14garage]

Cell defects. Super widespread on the Cayenne as well.

Bingo.

 

[Scandinavian]

That's cuz it's drained and not charged by the car, that's the real issue, software related.
If it gets below a certain voltage treshold the BMS of the 12V battery is shutting down, end of battery (for normal people).

If it's charged by the car there are absolutely zero issues with the 12V batteries.
Mine's almost 6 years old, no problem.
It can sit for at least two weeks and it's still being charged by the car so my software is working ok and so does the battery.

My car is also 6 years old and has had the 12 volt battery replaced at least once before. But still have issues when leaving the car for more than a few weeks. The main battery does not seem to recharge the 12 volt battery as it should. I suspect this is due to the 12 volt battery being a LiFePO, which seem to have a very shallow voltage curve between 20% and 80% SoC. Seems the Porsche BMS can not detect the correct level of discharge until it is too late?

https://cdn.shopify.com/s/files/1/0746/0415/1079/files/12v-lifepo4-volttage-chart.jpg?v=1724395687

It is now dead on my driveway after 8 weeks standing and no way to get into the car at all. The emergency key in the drivers door does nothing, it turns but there is no mechanical linkage. Only way now for me would be a crowbar to get into the frunk or open the door. But I will let Porsche handle that.

Porsche Assistance indicated that my car was in a queue to get into the service centre since it has been quite cold here for French conditions. Plus minus 0 C!

 

[Lee Chiacos]

Lordy, eight weeks of standing out in the cold in a driveway! Why would you expect anything different?

 

[Scandinavian]

Lordy, eight weeks of standing out in the cold in a driveway! Why would you expect anything different?

The average temperature during the 8 weeks was around 10 C, which as forfarande is not that cold. Only the last couple of nights have been colder but day time temperature about 14 C! If a car can not manage that it is not fit for purpose in my view.

 

[Dee]

My car is also 6 years old and has had the 12 volt battery replaced at least once before. But still have issues when leaving the car for more than a few weeks. The main battery does not seem to recharge the 12 volt battery as it should. I suspect this is due to the 12 volt battery being a LiFePO, which seem to have a very shallow voltage curve between 20% and 80% SoC. Seems the Porsche BMS can not detect the correct level of discharge until it is too late?

https://cdn.shopify.com/s/files/1/0746/0415/1079/files/12v-lifepo4-volttage-chart.jpg?v=1724395687

It is now dead on my driveway after 8 weeks standing and no way to get into the car at all. The emergency key in the drivers door does nothing, it turns but there is no mechanical linkage. Only way now for me would be a crowbar to get into the frunk or open the door. But I will let Porsche handle that.

Porsche Assistance indicated that my car was in a queue to get into the service centre since it has been quite cold here for French conditions. Plus minus 0 C!

It's not the battery, it's the car.

 

[Taycanistra]

We have here in Croatia EV clinic company which says the same: baterry from A123 system is a big shit!

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