Aux Battery Malfunction warning

[Gambell]

Hi, I'm new to the chat, bought a 2018 MP a few months ago and have spent quite a lot of time fixing some issues myself and resorted to a garage for the more difficult ones! I thought I was out of the woods and now the Aux Battery Malfunction warning comes up most days. It also prevents the cruise control from working. From what I understand the Aux battery is a the small motorbike battery under the drivers seat and accessed from behind the seat. It looks difficult to get out but I managed to get a volt meter across the terminals while in situ and its reading 12.8V with the engine off. Has anyone else had this problem and if so what was the solution? There does appear to be a small component fixed to the side of the battery box which is connected to + side of the battery (see photo). Maybe this is a voltage regulator. The output from this was 12.4V.

 

[Scrumpy]

I had mine replaced on Monday.
Warning message came on just before its
B service last week.
New battery was £109 + labour
The mechanic did say it was bugger to do because of where it sits

 

[Gambell]

I had mine replaced on Monday.
Warning message came on just before its
B service last week.
New battery was £109 + labour
The mechanic did say it was bugger to do because of where it sits

That's good to know. I tried to get mine out, virtually impossible. It's like keyhole surgery. You also need insulated socket wrench otherwise there would be sparks everywhere when you try and remove the cables from the battery terminals.

 

[Rob2]

Als accu niet meer goed is werkt de koelkast als eertste niet meer.

 

[j200george]

I thought although it was a tight fit it was supposed to be a diy task.

 

[peter_h4]

I’m confused.

My auxiliary/leisure battery is under the passenger seat in my right hand drive UK version. It’s a full size battery as opposed to a motorcycle size and I have removed it before to photograph the details and measure it as I have had a couple of malfunction warnings and have been suspicious of it’s reliability for a while now.

There isn’t another smaller battery hidden somewhere is there?

I have a 2017 MP.

 

[Scrumpy]

I thought although it was a tight fit it was supposed to be a diy task.

I’m sure with tools, work space, no kids etc.
mechanic said just a pain to work on.

 

[Scrumpy]

I’m confused.

My auxiliary/leisure battery is under the passenger seat in my right hand drive UK version. It’s a full size battery as opposed to a motorcycle size and I have removed it before to photograph the details and measure it as I have had a couple of malfunction warnings and have been suspicious of it’s reliability for a while now.

There isn’t another smaller battery hidden somewhere is there?

I have a 2017 MP.

Yes
MB use a second under the drivers seat.
Pull plastic cover off and you’ll see it. Similar to bike battery.
Is a back up to main battery, helps with stop/start etc

 

[peter_h4]

Ok so I found my auxiliary battery and have removed it to measure and test.

Getting a huge 10.8v after a pretty long run, so it’s about done. Measured it carefully and it needs to be no more than 130mm high due to constraints of the battery box. Plenty available at 145mm height, which is no good, but 130mm seems almost impossible to find (apart from official dealers of course at double the price)

Has anyone managed to source a suitable replacement?

 

[j200george]

Don’t know if you’re on the Facebook group. If not join that and search, it’s a well discussed topic. I posted here the other day but that might have been start/stop battery and I don’t want to confuse matters. (Like why this just went into italics) who knows.

I’d also check out Costco if you are a member once you get the specifications or try a local Indy car electrics place.

 

[peter_h4]

Thanks for that. I’ve now joined the group and good luck with your italics.