CHARGING AUXILIARY BATTERY

[Rievaulx]

I wonder anyone can help enlighten me re. the following, please? Question is about the auxiliary battery in my 21- plated MP.

Took the van into dealer a couple of months ago while still under warranty because of loss of MBAC functionality – the icon appeared on the head unit but didn't work (other functions such a 'phone and navigation all OK), so no fridge, pop-up roof operation, etc.

Diagnosis was that auxiliary battery needed to be replaced - and I was charged for it. It was claimed that the original battery could not be revived.

Since then it has become apparent that the aux battery level of charge gradually declines and is not being topped up by driving, even during long trips. I can however return it to 100% by plugging into an external electricity source via the “umbilical”. My suspicion is that the alternator is not doing its job, but I am absolutely not technically competent to be sure! More to the point I suspect that was the cause of the original problem, but not identified when dealer last had the vehicle. Makes me wonder if I've been ripped off!

Dealer suggests I bring the van in again, but won't commit about whether I'll end up being billed again.

I should be grateful for any comments and/or suggestions!

 

[Grumpy Mumble]

Do you have any way of measuring the voltage at the battery terminals, are you in possession of a basic multimeter?

 

[Rievaulx]

Do you have any way of measuring the voltage at the battery terminals, are you in possession of a basic multimeter?

Thanks for your interest! Short answer is: no, and no. I base my observations on MBAC display only. Was wondering, though, if my "duff alternator" theory had any merit.

 

[Sand]

I wonder anyone can help enlighten me re. the following, please? Question is about the auxiliary battery in my 21- plated MP.

Took the van into dealer a couple of months ago while still under warranty because of loss of MBAC functionality – the icon appeared on the head unit but didn't work (other functions such a 'phone and navigation all OK), so no fridge, pop-up roof operation, etc.

Diagnosis was that auxiliary battery needed to be replaced - and I was charged for it. It was claimed that the original battery could not be revived.

Since then it has become apparent that the aux battery level of charge gradually declines and is not being topped up by driving, even during long trips. I can however return it to 100% by plugging into an external electricity source via the “umbilical”. My suspicion is that the alternator is not doing its job, but I am absolutely not technically competent to be sure! More to the point I suspect that was the cause of the original problem, but not identified when dealer last had the vehicle. Makes me wonder if I've been ripped off!

Dealer suggests I bring the van in again, but won't commit about whether I'll end up being billed again.

I should be grateful for any comments and/or suggestions!

I have a 71 plate MP (second owner). Took mine in to dealer as aux battery wouldn’t charge above 70%. They replaced it straight away under warranty & no charge. Recommendation is to put it on EHU once a week for it to reach 100%.

 

[Grumpy Mumble]

Thanks for your interest! Short answer is: no, and no. I base my observations on MBAC display only. Was wondering, though, if my "duff alternator" theory had any merit.

Without knowing what volts are getting to the auxiliary/ leisure battery it is hard to say. I would suspect that if the alternator was duff all your electrical reserves would fail to charge. I haven’t looked yet but I am guessing that there will be a charge controller somewhere that will prioritise the main battery to charge first, and then when full switch to charge the auxiliary battery. I would be looking here first rather than the alternator if the van is starting okay.
If you could beg/borrow/steal but then give it back, a multimeter that could save you a lot of unnecessary flannel from MB about what it may or may not be.

 

[PeteS]

Did they replace the auxiliary battery. If they did then I would take it back and say that it is still doing the same thing. You could talk to them to say that you are unhappy with having a replacement battery it did not fix the problem.

 

[The fat controller]

The aux battery does require charging via the external cable at intervals to keep it in condition. Once a month would be the minimum I'd suggest. Long drives will help if you do them often but as grumpy mumble says above the van will charge the main battery first.

 

[IJB]

I wonder anyone can help enlighten me re. the following, please? Question is about the auxiliary battery in my 21- plated MP.

Took the van into dealer a couple of months ago while still under warranty because of loss of MBAC functionality – the icon appeared on the head unit but didn't work (other functions such a 'phone and navigation all OK), so no fridge, pop-up roof operation, etc.

Diagnosis was that auxiliary battery needed to be replaced - and I was charged for it. It was claimed that the original battery could not be revived.

Since then it has become apparent that the aux battery level of charge gradually declines and is not being topped up by driving, even during long trips. I can however return it to 100% by plugging into an external electricity source via the “umbilical”. My suspicion is that the alternator is not doing its job, but I am absolutely not technically competent to be sure! More to the point I suspect that was the cause of the original problem, but not identified when dealer last had the vehicle. Makes me wonder if I've been ripped off!

Dealer suggests I bring the van in again, but won't commit about whether I'll end up being billed again.

I should be grateful for any comments and/or suggestions!

Hi. A word of caution from our own experience less than three weeks ago. Our aux battery in our 2020 v300d was not holding a charge from driving or holding the whole charge from the hook up overnight. The night before a weekend away I put the hookup on overnight . 50 miles into the trip the passenger seat heated up, steam on that window and sulphuric smell. We pulled into M3 services and called out MB breakdown. They came out in around two hours. The MB /RAC person said we were lucky the battery had not gone bang. He gingerly pulled it out from under the seat and disconnected it. We drove on ok without the lack of aux battery affecting any othe function. He told us the aux battery needs trickle charging regularly . The MP goes in for service next week and they will fit a new aux battery and indicated this would be under warranty. The MB breakdown guy suggested buying a CTech trickle charger, though the the practicality of connecting this seems ….impractical. I’m thinking the orange hookup lead would be best for regular charging when we are not using the MP all that often.

 

[Sand]

The aux battery does require charging via the external cable at intervals to keep it in condition. Once a month would be the minimum I'd suggest. Long drives will help if you do them often but as grumpy mumble says above the van will charge the main battery first.

We have a 21 plate V330d bought second hand. The Aux battery wouldn’t charge over 70% when plugged in via EHU or driven for miles. Contacted local Mercedes dealer (Exeter) and they had no hesitation in replacing the battery without any charge as it was under warranty. For info: Exeter branch have also replaced the table under warranty and we are in the process of having the rear blackout blind replaced under warranty.

 

[Steve B]

The MB breakdown guy suggested buying a CTech trickle charger, though the the practicality of connecting this seems ….impractical. I’m thinking the orange hookup lead would be best for regular charging when we are not using the MP all that often.

I'm sure the hook up at home would be fine, you see many motor homes on peoples drives hooked up. Ours is a daily driver so constant charge and the battery seems little different today as a few years ago.