Battery keeps saying Low when I start the car

[JamesR27]

Hi All,
I am after a bit of advise, car is only really used on weekends and just over a week ago I did 450 miles in it on a overnight trip. Started the car up yesterday and it kept telling me my battery was low. I would have thought that would be good for a good charge.

I was thinking of putting it on charge but need to buy a battery charger. What do people recommend?

[kenny.c]

Just curious......is the car standard...?? In other words you dont have a DTUK tuning box on it do you..?
If your after a charger just be sure it does AGM bateries not just normal lead acid.

You may be able to check the SOT (state of charge) by doing the following.
- Get in the car and shut the door
- Dont put the ignition on
- Press and hold the 0.0 trip reset button in the instrument cluster
- It will cycle through the trip then it will show the Battery SOT
- Release and then the display may show the SOT as a percentage

I say "may" as some cars need this function activating in VAGCOM others dont like mine

Your VW dealer can reset the battery monitoring system which basically involves fully charing the battery and telling the car its fully charged.

Thanks
Ken

[JamesR27]

Hi,

Thanks for the reply. Yes the car is completely standard. I will give that a go tonight though and see what happens.

[itavaltalainen]

Sure it's not a message for the key fob battery? Not seen either yet myself, just thinking.....

[Exonian]

I had a replacement battery last year after getting similar warnings when I started the car.
It went from there to getting a flat battery and I had a replacement battery when the car had its first service.
I wasn't using the car very often at the time. I make sure I try and use it more nowadays.

[JamesR27]

You may be able to check the SOT (state of charge) by doing the following.
- Get in the car and shut the door
- Dont put the ignition on
- Press and hold the 0.0 trip reset button in the instrument cluster
- It will cycle through the trip then it will show the Battery SOT
- Release and then the display may show the SOT as a percentage

Thanks for the advise, I tried this when I got home and it worked and showed 40% charge

[dv52]

James: All that OPs have said is good sensible advice, but I'd like to add another dimension to your low battery situation and  say a word, or two about correctly charging the battery on a mk7.

All of what I'm about to say relates to those mk7's that have either the Stop/Start system (it's called "bluemotion" down here - not sure if the same badging happens elsewhere), or an energy recovery mechanism. These cars have a "battery sensor"  that is fitted in-line into the negative battery cable just next-to the battery clamp. The battery sensor (called J367 by VW) also has a connection to a control module called  the "Data bus diagnostic interface".

The role of the battery sensor is to determine the condition of the battery (i.e.voltage, current and temperature) and this information is sent to the diagnostic interface in the car. Through this sensor and the previous history of data that it has sent, the diagnostic interface builds-up a picture of the current capacity in the battery. The SOC reading that kenny_c has mentioned is a measure of the past history of the battery since it was first installed in your car and all the direct battery data came from the "battery sensor".

VW make a distinction between the voltage at the battery and what it calls the "System Voltage", which is the calculated voltage that is available to the car's actual electrical system. All the decisions that are made by the car that reference voltage are taken from the "System Voltage" (not the battery voltage). So, it's real important to maintain the veracity of the System Voltage and incorrectly charging the battery is one way to f&*^k-up this value.

With ANY VW vehicle with bluemotion or an energy recovery mechanism, you should NOT connect the battery charger negative clamp to the negative battery terminal. Doing this by-passes the battery sensor. This means that the battery data is not recorded by the sensor during the charging procedure. The values for the battery state stored in the data bus diagnostic interface then no longer coincide with the real values of the charged battery. 

In cars with SS ALWAYS connect the positive charger clamp to the battery positive terminal first. then connect the  clamp on the battery charger negative to an earthing point in the car (like a metal component that is screwed to the engine block).  This also applies if you are jump-starting the car.

[Juicetin]

DV52, that is useful information, thank you. My battery charger (CSI Airflow) connects to + and - terminals so it is good to know that this should not be followed in the Mk7 with start stop.
Thank you.

[kenny.c]

James: All that OPs have said is good sensible advice, but I'd like to add another dimension to your low battery situation and  say a word, or two about correctly charging the battery on a mk7.

All of what I'm about to say relates to those mk7's that have either the Stop/Start system (it's called "bluemotion" down here - not sure if the same badging happens elsewhere), or an energy recovery mechanism. These cars have a "battery sensor"  that is fitted in-line into the negative battery cable just next-to the battery clamp. The role of the battery sensor is to determine the condition of the battery (i.e.voltage, current and temperature) and this information is sent to the diagnostic interface in the car. Through this sensor and the previous history of data that it has sent, the diagnostic interface builds-up a picture of the current capacity in the battery. The SOC reading that kenny_c has mentioned is a measure of the past history of the battery since it was first installed in your car and all the direct battery data came from the "battery sensor".

VW make a distinction between the voltage at the battery and what it calls the "System Voltage", which is the calculated voltage that is available to the car's actual electrical system. All the decisions that are made by the car that reference voltage are taken from the "System Voltage" (not the battery voltage). So, it's real important to maintain the veracity of the System Voltage and incorrectly charging the battery is one way to f&*^k-up this value.

With ANY VW vehicle with bluemotion or an energy recovery mechanism, you should NOT connect the battery charger negative clamp to the negative battery terminal. Doing this by-passes the battery sensor. This means that the battery data is not recorded by the sensor during the charging procedure. The values for the battery state stored in the data bus diagnostic interface then no longer coincide with the real values of the charged battery. 

In cars with SS ALWAYS connect the positive charger clamp to the battery positive terminal first. then connect the  clamp on the battery charger negative to an earthing point in the car (like a metal component that is screwed to the engine block).  This also applies if you are jump-starting the car.

Great info.....thanks for sharing