Main or aux battery causing niggles?

[Hans red]

Hi I have a 2012 w204 c class.

I have started getting more and more electrical issues that have started intermittent and now become permanent.

1. start/stop has not worked for a year or so
2. Automatic door unlocking no longer works, the doors lock when I start driving but do not unlock when I open the drivers door. This slowly stopped
3. The long press brake hold no longer works. Again this slowly worked less and less often.

These have all started fading out over time which says to me it’s the battery. But I’m not sure which one.

the main battery shows max of 11.8v on the instrument cluster (goes up with the engine running) had it on charge all day and it didn’t go above this.

does it sound like the main battery that would cause this kind of behaviour or is it more likely the aux battery? (Or neither)

thanks in advance for any thoughts...

 

[Blobcat]

Hello and welcome,

Battery should be ~12.6v at rest and +14V on charge - get the battery changed and see how it goes after that

 

[jimbg]

New battery.....

 

[Hans red]

The chart kind of puts it into perspective. Surprised it’s even cranking it at 10% battery!

guess I’ll bite the bullet and get a new one. Any recommendations? Tayna do an enduroline one for around £120 is it worth cutting corners?

 

[NJS5]

Tayna are good, but returns are difficult if there are problems.

I have used Halfords for batteries for some time; 5 year warranty, but you MUST produce the receipt if you are to claim.

I put a laminated copy of the receipt alongside, or underneath the battery.

NJSS

 

[Blobcat]

Tayna are good, but returns are difficult if there are problems.

I have used Halfords for batteries for some time; 5 year warranty, but you MUST produce the receipt if you are to claim.

I put a laminated copy of the receipt alongside, or underneath the battery.

NJSS

I wouldn't go near Halfords for a battery...
Quite a few recommendations from members on the forum, worth a search

 

[ajlsl600]

Varta. Also read yr codes on car with star or decent reader if you have loads of faults .under voltage reports that will give you a good idea.note them all then clear them modern cars ,benz do not like low batts many an issue can stem from this.

 

[Hans red]

I did get the codes read by star a few months back but there were apparently lots in there, so they cleared it and said pop it back in a week or so and they would read again, but then they were busy and wanted it booked in again and I just didn’t have time to leave it another day.. now that it’s got worse I wish I had, but it is all pointing to the battery so I’ll just get it done.

 

[Gazwould]

I wouldn't go near Halfords for a battery...
Quite a few recommendations from members on the forum, worth a search

They do Yuasa which is a sound choice .

An easy return if problems are experienced .

 

[Hans red]

Halfords is only showing their own make currently, is that just a re brand? I’ll also give my local auto spares a shot, see how much they can do one for. Support the little guys and all that... Can I just whop a new battery in or does it need programming?

 

[EmilysDad]

Halfords is only showing their own make currently, is that just a re brand? I’ll also give my local auto spares a shot, see how much they can do one for. Support the little guys and all that... Can I just whop a new battery in or does it need programming?

there are a million & 1 places I'd go to before I went to Halfords ... unless I needed something late on a Sunday afternoon. They're expensive & the majority of their staff are clueless

 

[AMGeed]

Get a quote from your main dealer after noting the Mercedes Part# if its an original battery.
If you have a Mercedes Commercial dealer, try them.
Should be even cheaper than the car main dealer.

Also, check the price on ECP with their never ending discount code.

I'd also check the condition of your aux battery, especially if it's the original.
On my E55, the hold feature stopped working when the aux battery went bad.

 

[Taffy7hfa]

I reckon 20% of all the problems posted on the forum relate to failing batteries

 

[Hans red]

Get a quote from your main dealer after noting the Mercedes Part# if its an original battery.
If you have a Mercedes Commercial dealer, try them.
Should be even cheaper than the car main dealer.

Also, check the price on ECP with their never ending discount code.

I'd also check the condition of your aux battery, especially if it's the original.
On my E55, the hold feature stopped working when the aux battery went bad.

I’ll have a phone around tomorrow, and also get the volt meter on the aux battery. I tested some load by leaving the residual heater on today and that was still going after 10 mins, but the radio turns off in less than 5. Just not sure what draws from what battery and how it’s all balanced. The power socket in the boot only works for a minute or two as well with ignition off, whereas the front one is fine with ignition on poition1

 

[Tony Dyson]

The chances are both your batteries are still original, look for id stickers on the top or side elevations for a Date stamp or sometimes punched into the top of the lead connection pillars it will be in the format of Week No/Year i.e. 25/12, I would replace both in this case. Your batteries I suspect will be AGM/VRLA, it is important they are replaced with batteries of the same chemistry to avoid complications and get the best performance from the charging profile provided by your car, check the spec's below for compatibility with your existing?

https://www.tayna.co.uk/car-batteries/varta/f21/
https://www.tayna.co.uk/car-batteries/varta/aux14/

 

[mioba]

Merc original batteries are very good. They lasted what 8 years, The original on my w220 lasted 12 years. If the cars a keeper go original.

 

[Bay Leaf]

I've read on another forum if your Aux battery is suspect the stop/start wont work and neither will the brake hold facility. I tried to copy the post for you but to no avail.

BL

 

[Gazwould]

Brake HOLD has nothing to do with the aux battery .

I've done this...

 

[Hans red]

The whole thing feels like a delicately balanced eco system with very specific tolerances. Didn’t get a chance to check the aux battery today but will get a reading tomorrow. Although I read somewhere that if the main battery is struggling then the aux battery will not get so much charge as it gets pushed down the pecking order for charge resource.

 

[Gazwould]

There's loads of factors , brake booster sensor included .