W211 backup battery not charging

[jasonyw]

It 1.1V according to STAR, do I need to replace it?

or can I recharge it from the main as it not charging while driving it.

 

[AndyPCD]

Have you checked the actual voltage of the battery itself with a multimeter

 

[Diesel Benz]

It 1.1V according to STAR, do I need to replace it?

or can I recharge it from the main as it not charging while driving it.

Quite likely the battery has been affected and needs to be replaced but that cannot be enough if it is the same when the car is running. Must be an issue with the AUX battery relay too?

 

[jasonyw]

Have you checked the actual voltage of the battery itself with a multimeter

I used a multimeter, both at least 12V, must be something wrong with the STAR, crap software.

 

[Diesel Benz]

I used a multimeter, both at least 12V, must be something wrong with the STAR, crap software.

Was that measured when the AUX battery relay was open? It is not obvious when the relay is open or closed and if it is closed, you would measure the same voltage from both batteries even if the AUX battery was completely gone.

 

[jasonyw]

Was that measured when the AUX battery relay was open? It is not obvious when the relay is open or closed and if it is closed, you would measure the same voltage from both batteries even if the AUX battery was completely gone.

How do I know whether the relay is open or closes?

 

[AndyPCD]

The easiest thing to do it disconnect the aux battery and test the voltage of the battery that way.

One thing that springs to mind it there is a wire that runs from under the aux battery to the battery control module. Due to the positioning of the wire it tends to rot through and doesnt send a correct signal to the control module

 

[jasonyw]

The easiest thing to do it disconnect the aux battery and test the voltage of the battery that way.

One thing that springs to mind it there is a wire that runs from under the aux battery to the battery control module. Due to the positioning of the wire it tends to rot through and doesnt send a correct signal to the control module

There is a jumble of wires in the booth, don't know which wires go.
Is there a circuit diagram somewhere?

 

[AndyPCD]

Did you check the voltage of the battery disconnected

 

[jasonyw]

Have you checked the actual voltage of the battery itself with a multimeter

I did take the opportunity to measure it today after 1,300 miles, 12.53volts, it did charged after all after being driven but you cannot charge it with the household charger, I gathered somewhere.

I did not connect up the aux battery, immediately Visit workshop is displayed when I started up the engine. It not really an aux battery, it essential, without it, there will be no SBC!