Uwe: Of course I always bow to the superior and awesome knowledge of RT folk, but my understanding (based on my reading of VW's scant literature on this topic) is similar to yours: if the monitoring module is installed, the vehicle keeps a history file of the battery current-in/current-out which is fodder for VW's magic and highly secretive algorithm that then calculates the variables. Again, I will take advice from RT, but on vehicles like the mk7, I believe that it's possible to reset the historic table by changing the battery serial number that is recorded in the CAN Gateway. I've found that the actual serial number entered isn't important - it just needs to be different to the previous entry.
Does fussybob's (love the handle) car have a similar facility - if not, how does the CAN Gateway become aware of a battery change?
Don
PS: Given that the battery history table is built-up over the life of the battery, it seems reasonable to assume that the veracity of the calculated variables is necessarily, very dependent on the owner's practices (as they relate to the battery) - I believe. So, stuff like how an external battery charger, or how the car is jump-started is crucial to the accuracy of the table values. If, for example, the negative lead of an "external power source" is incorrectly connected to the car (i.e. it's connected directly to the negative battery terminal), then it stands to reason that the stored current-in/current-out variables in the table will be wrong (because the battery monitor module is by-passed) -which means that the calculated variables will also be wrong for the life of the battery (I think). Happy to hear from others about this - I'm always willing to learn!!
Yes you need to change at least 1 digit in the serial number to reset the battery history table with a new battery change.
Some Power Management info below. Guess we need the engineer that developed this to explain the complexity.
History data......
The diagnosis tester can be used to read out
data from the control unit for power management,
which makes it much easier to analyse the on-board
power supply and the battery.
Open-circuit voltage history
If the battery open-circuit voltage is less than the
threshold values of 12.5 volts, 12.2 volts and
11.5 volts, an entry is written to the history data.
The last four entries can always be read out.
Voltage measurement starts when
– CAN Convenience is in Sleep mode and
– terminal 15 is switched off for at least 2 hours
and
– the vehicle’s power consumption is < 100 mA.
Voltage measurement ends when
– the voltage increases or
– the current increases or
– the control unit triggers Sleep mode or
– the control unit detects a new battery.
Closed-circuit current history
If the closed-circuit current exceeds the threshold
value of 50 mA, an entry is written to the history
data. The last ten entries can be read out.
Current measurement starts when
– CAN Convenience is in Sleep mode and
– terminal 15 is switched off for at least 2 hours
and
– the vehicle’s power consumption is > 50 mA.
Current measurement ends when
– the current decreases or
– the control unit triggers Sleep mode.
Breakdown analysis
If the control unit for power management detects
the status "Cannot start vehicle", an entry is written
to the history data.
Battery change
Data for the last three battery changes is stored.
Power balance history – driving (= engine on)
The power balance and duration of the last five
journeys are logged.
Power balance history – idle (= engine off)
The power balance and duration of the last five idle
times are logged.
Other data is not relevant for Customer Service