Leisure battery not charging while driving

funkyegg said:
Please can anyone confirm what the leisure battery voltage should be when the car is running ? Thanks

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I think it depends how charged it is.

On mine, if it's low (like half) then you get around 14.4v (i.e. alternator voltage)

If it's nearly full it seems to be about 13.1v when driving and then sometimes 12.8v, which is, I assume the charger changing to a 'trickle charge' mode. I don't believe it's directly connected to the alternator, or it may be that it is and the alternator is 'smart' (which is could well be to reduce fuel consumption / emissions)
 
Brian Drought said:
I think it depends how charged it is.

On mine, if it's low (like half) then you get around 14.4v (i.e. alternator voltage)

If it's nearly full it seems to be about 13.1v when driving and then sometimes 12.8v, which is, I assume the charger changing to a 'trickle charge' mode. I don't believe it's directly connected to the alternator, or it may be that it is and the alternator is 'smart' (which is could well be to reduce fuel consumption / emissions)
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Cheers Brian. Does the voltage increase as soon as you turn on the engine?

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14.2 to 14.7 would be normal voltage...

I'm sorry to say though that all this science is totally academic...

The vehicle is supposed to charge the leisure batteries when moving. It does not charge when moving. There is therefore a fault. MB... sort it.

There should never be any need to ever ask these questions: as we speak hundreds of thousands of motorhomes, campers, awesome conversions and unbelievable creations are running around with the vehicle alternator through relays charging both starter and leisure batteries. Even the most crass, horrible, cheap and nasty self-build can do it so please Mr magical Mercedes Benz you can do it. Fix it. End of story.
 
BabaJen said:
14.2 to 14.7 would be normal voltage...

I'm sorry to say though that all this science is totally academic...

The vehicle is supposed to charge the leisure batteries when moving. It does not charge when moving. There is therefore a fault. MB... sort it.

There should never be any need to ever ask these questions: as we speak hundreds of thousands of motorhomes, campers, awesome conversions and unbelievable creations are running around with the vehicle alternator through relays charging both starter and leisure batteries. Even the most crass, horrible, cheap and nasty self-build can do it so please Mr magical Mercedes Benz you can do it. Fix it. End of story.
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A very valid point and as quite rightly pointed out-unacceptable.

MB dealers should know these vehicles inside out,every last detail and yet they don’t-far from it in fact.
 
Brian Drought said:
Not always no. It's not as simple as 'engine running, see alternator voltage'.
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Fair enough, if you read my reply it was not really about technicalities as to point out it's not rocket science and something MB should sort and stop messing a "valued" customer around.
 
BabaJen said:
14.2 to 14.7 would be normal voltage...

I'm sorry to say though that all this science is totally academic...

The vehicle is supposed to charge the leisure batteries when moving. It does not charge when moving. There is therefore a fault. MB... sort it.

There should never be any need to ever ask these questions: as we speak hundreds of thousands of motorhomes, campers, awesome conversions and unbelievable creations are running around with the vehicle alternator through relays charging both starter and leisure batteries. Even the most crass, horrible, cheap and nasty self-build can do it so please Mr magical Mercedes Benz you can do it. Fix it. End of story.
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Totally agree. I'm due to collect my vehicle for the fifth time within a month for the same battery issue after they updated the front SAM, replaced relay and battery fuse box and I think they finally fixed it but I can only confirm after a road test this weekend... Hopefully, after fixing my issue Mercedes Epsom is now experienced in fixing all battery related issues with the MP. It has been very stressful as I wasted a good part of the summer going back and forth with the dealership for the same issue and it took me long time to convince them that the leisure battery wasn't charging and they had done two extended roadtests for their technicians to drive my vehicle back to their homes after work to admit the issue. Thanks to this forum that I was able to share the information with the dealership to point them to the possible solutions and to have it fixed after 5 attempts. I'm guessing in the end the issue was probably caused by something like a blown fuse...could have been easier but that's just life...

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