Hi everyone, I wanted to share my experience in case it helps someone else with the same issue.
My car is a vw Tiguan 2020
I recently replaced the battery with a new AGM battery and properly coded/adapted it using VCDS.
However, I kept getting: “12V battery low” warning, Keyless entry randomly stopped working, Battery voltage looked completely normal (12.7–12.9V engine off, ~14.8V charging).
At first I thought it was: bad battery coding, alternator, parasitic drain, ignition misfire, LED conversion, gateway module
But after a lot of testing, I found the real issue was the IBS (Intelligent Battery Sensor) on the negative battery terminal.
What finally confirmed it
I unplugged the IBS connector and drove the car normally.
With the IBS unplugged: • no more battery low warning • keyless worked normally • battery voltage stayed stable overnight • car behaved perfectly fine
Then I plugged the IBS back in: after a short drive, keyless stopped working again immediately.
That pretty much confirmed the IBS was sending incorrect SOC/battery data to the car.
I replaced the negative battery cable / IBS assembly: 5QA 915 181 D(very easy to install)
The battery adaptation I had already done stayed valid.
Hopefully this helps someone else avoid replacing random parts like alternators or batteries unnecessarily.