As far as I can tell, if I charge the battery with a CTEK charger through the charging points in the engine bay the auxiliary battery does not charge at the same time. Therefore if the car is left for long periods even though the CTEK is connected and the main battery is fine the auxiliary one goes flat.

Does anyone know how to charge the auxiliary battery safely? From what I can tell this is a much smaller battery than a normal car battery and sits in the boot on the right hand side with lots of other electronic stuff.

Will it not get charged once the vehicle is started from the main battery? Current: RR L322 2010
Past: RR L405 2017, RR L322 2012, 2008 & 2004, 2018 D5, 2016 Defender, 2011 D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB

I'm not sure how they connect - will need to have a play with a meter on them.

My boat has dual batteries & they connect together & both charge above a certain voltage & disconnect below it. So whenever the alternator is running, or a charger connected, they both charge. Not sure whether the RR has something similar....

Yes a voltage sensing relay (VSR).

Maybe you aren't charging it with a high enough voltage to trigger the VSR? Current: RR L322 2010
Past: RR L405 2017, RR L322 2012, 2008 & 2004, 2018 D5, 2016 Defender, 2011 D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB

the aux battery is for the stop/start, if you dont like that feature then disconnect it or leave it flat.. ... - .- -.




Y. O. L. O.
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It must do more than stop/start - I don't have that feature on mine, but I have an auxiliary battery.....

If it just did stop/start I would happily disconnect it but I think it does more.

Is there any technical reason why I shouldn't connect my CTEK to the terminals on the auxiliary battery?

connecting directly will probably cause problems with the BMS [battery monitoring system]

take it out and bench charge...... ... - .- -.




Y. O. L. O.
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Also you shouldn't charge a battery in a vehicle (esp in the passenger compartment).

You are selecting it as an AGM battery when charging? How do you know it's flat? Current: RR L322 2010
Past: RR L405 2017, RR L322 2012, 2008 & 2004, 2018 D5, 2016 Defender, 2011 D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB

I don't know its flat for sure but I know the main battery is fine because it is on the CTEK and the car starts fine and everything seems to be OK. However I get a battery warning on the dash. Also the tailgate does not operate automatically. If I drive it long enough all these things go away so I thought it might be the aux battery going flat once the car has been left for a couple of months even though the main battery is on the charger.

And you are charging it as an AGM battery on the ctek? Current: RR L322 2010
Past: RR L405 2017, RR L322 2012, 2008 & 2004, 2018 D5, 2016 Defender, 2011 D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB

I don't know for sure. I just have the car icon selected on the options.

Just got the instructions out. No. I am not using the AGM option. Should I be doing this?

Assuming they are all AGM batteries so would have thought so. Current: RR L322 2010
Past: RR L405 2017, RR L322 2012, 2008 & 2004, 2018 D5, 2016 Defender, 2011 D4, a few Disco2s, P38, RR Classic, couple of Disco1's, SIII SWB

I charged it using the higher voltage setting and that seems to have done the trick.

Thanks for your help!