Thread: Has anybody fitted a Lithium Cranking Battery to their D4.

Hi mate,
I have a lithium battery in my beast but its a 03 RR TD6. Am thinking of getting a Skoda Kodiak later this year so am
interested in the replies.
If your not using it for a day or three,what about putting it on to solar for a charge up.
Would imagine that the Skoda would use same sort of alternator as the veedub.

cheers
DG

HI DG, the D4 own electrical needs draw up to 40 amps while driving, and I want to see if any body has managed to turn off/disable the D4’s SMART alternator function?

The problem is that when the D4’s BMS ( Battery Management System ) detects a fully charged cranking battery, the BMS runs the alternator at a much lower operating voltage.

When a lithium battery is in the system, either as the cranking battery or as an auxiliary battery, because lithium batteries run at a constant 13.3v until they are nearly discharged ( down below 20% SoC ) the D4’s BMS incorrectly reads this 13.3v, being supplied from the lithium battery, as a fully charged cranking battery.

In a normal lead acid battery setup, as the alternator voltage drops, so does the lead acid cranking battery.

If the lead acid cranking battery drops to a LOADED voltage of 12.3v, approximately at 70% SoC, the alternator voltage will automatically rise to allow the cranking battery to be recharged.

With a lithium battery in the system, either cranking or auxiliary, the voltage remains at 13.3v and as the BMS incorrectly sees the cranking battery is fully charged, the alternator voltage remains low.

BUT, as the lithium battery voltage is higher than the alternator voltage, it is the lithium battery that is powering the D4.

Around town is not as much a problem, particularly with lots of short runs, as the BMS normally gives an initial high voltage boost, to replace the energy used by the cranking battery to start the motor.

This short boost also charges the lithium battery at the same time.

The real problem will come when the D4 is driven for a long period.

On long drives, which thanks to Covid lock-downs, I have not been able to do till just recently, in my Tiguan with the SMART alternator function turned on, after about 2 plus hours of driving, I suddenly found the lithium battery ( and cranking battery ) was down to 13.14v while driving.

This indicated that the Tiguan was being powered by the lithium battery and the alternator was literally Free-wheeling.

I was on a relative long drive, when I noticed the low voltage, 13.14v, so I stopped, deactivated the SMART alternator function and the voltage rose to 13.6v and remained between 13.6 and 14.3v on the return home trip.


The SMART alternator function has remained off for a few weeks now and the two batteries has a settled voltage ( motor off ) of 13.3v at all times.

This is the reason for the question of whether any one has a D4 with a LITHIUM cranking battery.

Originally Posted by drivesafe

I want to see if any body has managed to turn off/disable the D4’s SMART alternator function?

It’d be interesting to see what voltage and faults are apparent if you pull the LIN line to the alternator.

Hi Brad, on the Tiguan, you simply disconnect the battery sensor plug on the cranking battery's negative terminal.

I wonder if it is as simple as that on a D4.

I originally disconnected the sensor plug because it deactivated the STOP/START function, but quickly found it raised the alternator voltage as well.

WIN WIN