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[Andy B]

I'll ask here .... better chance of a reply rather than the MB's forum standard reply of take it to a dealer/indie. 

If I wanted to use a CTek on my ML due to it standing more than normal, does anyone know if the auxiliary battery in the 'boot' get charged if I just connect the charger to the jumper connections under the bonnet? (starter battery lives under the driver's seat) Access to the aux battery requires dismantling of the boot liner/carpet.
I'm not really sure what the aux battery is for .... some suggest it's something to do with stop/start. 

[Doctor Gollum]

It provides power whilst the engine is off, saving the big battery for the big job

[Field Marshal Dr. Opti]

My CLS 500 had a second motorcycle sized battery. Never quite sure of it's purpose.

[Doctor Gollum]

It provides power whilst the engine is off, saving the big battery for the big job

[Andy B]

My CLS 500 had a second motorcycle sized battery. Never quite sure of it's purpose.

That's what mine is like, though you can only just about see it if you remove the cover that accesses the back of the rear lights.
Not sure how long it would provide power .... 

[Andy B]

so ..... does the aux battery charge from the jumper points? 

[Field Marshal Dr. Opti]

My CLS 500 had a second motorcycle sized battery. Never quite sure of it's purpose.

That's what mine is like, though you can only just about see it if you remove the cover that accesses the back of the rear lights.
Not sure how long it would provide power .... 

The Germans think it fun to make them difficult to get at.

[Doctor Gollum]

so ..... does the aux battery charge from the jumper points? 

Christ no AIUI, it keeps the climate control ticking over in REST mode and powers the radio. So apart from a couple of coolant pumps and a low blower speed, it doesn't actually need alot of power.

If I remember, I will have a look and see what WIS has to say about it.

[Raeturbo]

Well if that’s the case what keeps the little battery charged then?  If you can get a multimeter on it check it when you have the other one charging.

[Andy B]

so ..... does the aux battery charge from the jumper points? 

Christ no AIUI, it keeps the climate control ticking over in REST mode and powers the radio. So apart from a couple of coolant pumps and a low blower speed, it doesn't actually need alot of power.

If I remember, I will have a look and see what WIS has to say about it.

I didn't put it very well. Jumper points are obviously connected directly to main battery ..... 

[Andy B]

Well if that’s the case what keeps the little battery charged then?  If you can get a multimeter on it check it when you have the other one charging.

That's what I was trying to avoid 

https://www.youtube.com/watch?v=ATjTFgx2Yzs 

[Andy B]

I'll just use the car every other week 

[Doctor Gollum]

https://forums.mbclub.co.uk/threads/auxiliary-battery.200744/

[Andy B]

https://forums.mbclub.co.uk/threads/auxiliary-battery.200744/

I've seen that before, but some Mercs seem to have some kind of large capacitor instead and the web has conflicting info

[Doctor Gollum]

The facelift cars clearly have it in a different place too... Early cars GL have it under the right front seat behind the battery... Just to help