The scourge of the BEV. All EV manufscturers seem to have issues with the 12v system though 4 battery changes seems excessive. I just had mine replaced after 18 months for a transient brake pedal feel reduced error. I'm still not sure it was actually a problem with the battery - i have to trust the dealer on that one.

I read somewhere Tesla is looking to eliminate reliance on 12v batteries in the future but their cars have also been plagues by the same issue. I wonder if type of driving makes a difference - all short trips, or if only intermittent use kills the 12v more quickly in BEVs. A dc-DC converter is supposed to keep the 12v topped up when driving and charging i believe.

Hope you have no further issues going forward - it's a great car.

 

I'm no expert but my understanding is that there are good reasons for having a lead acid battery power the 12V system, as opposed to a Lithium battery. If the entire system were redesigned then perhaps a different type of battery could be used?

 

This happened to me & might explain something. I was testing some equipment, as directed & it acted like a bad ground with everything going off and power surging. It turns out the power supply I was using didn't provide 'storage power' (or what ever you want to call it) for testing use and needed a battery in it's circuit to complete test functions. I have an idea that with reduced voltages and currents, newer batteries just don't have the guts (industry term) and a lead acid battery might be the only answer. I know that on newer class 8 trucks, the bi-metal strip inside flasher units had to be re-designed. The newer lights didn't give enough current for them to run right. What do you think?

 

And now Porsche Taycan is being investigated for some loss of power which may be due to the 12 volt battery.

 

A few tidbits I've gathered online, so I cannot personally vouch for their accuracy but they make sense to me.

- BEVs need an auxiliary power source to be able to open and close the main relay or contactor to disconnect the traction battery when it's not in use for safety reasons. These are 12V for the time being because basically all of the existing vehicle electronics are designed for 12V, so it's easy to also use this battery to power the car's electronics.

- Lithium batteries require a computerized battery management system to keep them healthy and safe. Adding this to the auxiliary battery would be expensive, and perhaps leads to a "who watches the watchmen" sort of situation.

- Current automotive lead acid batteries are optimized for use in an ICE, where are major part of their function is to run the starter motor to start the ICE. They are perhaps not as well suited to use in a BEV which never sees these starter loads. I've read that this lack of hard use may lead to deposits on the plates in the battery which reduce its life expectancy.

 

The OP apparently is unaware of the 47 Ah starter battery that provides power to most of the items mentioned. The 15 Ah auxiliary battery is there to supply power for few control modules in pre-MY21 cars.
I find electrical system in the I-pace is quite complex after reading through parts of the workshop manual. Somebody forgot the keep-it-stupidly-simple principle.

The flooded battery (47 Ah) and AGM battery (15 Ah) get charged by the DC-DC converter. There is no alternator.

We all know that if 12V the battery is defective it won't charge, just as I've had happen on ICE vehicles. No/low power from the 12V system can definitely cause electronic modules to function in unexpected ways or not at all.

Additionally, I've also found note that the BMS (battery management sensor) mounted on the negative post makes note of the state of the battery on vehicle shutdown. If the BMS detects that the SOC drops 5% or more then it turns on the DC-DC converter to recharge the 12V battery from the traction battery back to the reference charge state. Now, based on that simple description, if the 12V battery has a low charge (think of a lot short trip driving without time to adequately recharge it) that shut down state of charge won't get the 12V battery recharged as it gradually gets a lower SOC for each short trip. An intentional external recharge might bring the 12V battery back to life, or it has depleted beyond the point of no return.

And one other thing, a defect in the DC-DC converter could also lead to no charging. And there's other modules involved that may have old programming that need updating to make it all work right.

Lithium, AGM or flooded won't make much difference if the rest of the system isn't working properly.

 

...Additionally, I've also found note that the BMS (battery management sensor) mounted on the negative post makes note of the state of the battery on vehicle shutdown. If the BMS detects that the SOC drops 5% or more then it turns on the DC-DC converter to recharge the 12V battery from the traction battery back to the reference charge state. Now, based on that simple description, if the 12V battery has a low charge (think of a lot short trip driving without time to adequately recharge it) that shut down state of charge won't get the 12V battery recharged as it gradually gets a lower SOC for each short trip...

This could be a very important point for consideration since the electronics come to life with an unlocking of the car, rather than a push of the "start" button. Possibly simple operations like opening the door and initiating a shut down and then returning to the car and sitting "playing" with the toys would lead the BMS to believe the auxilliary battery does not need charging. Repetition of such sequences, or short trips, could easily reduced the charge state of the battery in an iterative manner eventually leading to battery failure.
Do we know how quickly the DC-DC converter can charge the batteries? I feel I saw somewhere a recommendation to go for a 1hr drive if the batteries are reporting a low state of charge.

 

Interesting hypothesis. I don't know though, it doesn't make much sense to design the system that way. Maybe it's just poorly explained in the workshop manual?

Also, ICE cars have a 12V battery voltage display ... do we have that anywhere? Is WattCat's "Auxiliary Battery" the 12V system's?

 

So a weekly charge on a trickle charger might solve the problem?

 

The car should trickle charge the 12v battery from the traction battery through the DC to DC converter. When the 12v drops to 12.4 in my case it gets a charge as if the door is unlocked. If the 12 needs an external charge then the car needs the dealer to look at it.