Battery Problems Six Mo After Replacement - wasn’t expecting that

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New Member
Nov 26, 2022
CLS350 Grand Edition CDI (W219)
Hi Again Forum,

About six months ago, I got some helpful advice from Forum - Coincidence or something I’ve done - electrics playing up
The short version - consensus of opinion; retire my original battery (I didn’t realise age was stamped on it).
So I changed the battery; got an MB VARTA AGM from local MB for the same as after-market one.
Fitted it, cleared the faults, reset the windows and normal service was resumed …….and all was good again.

Six months later - it’s happened again; large battery warning symbol (after 50miles trip), central locking, fuel gauge, indicators all stopped….
I put battery on charge - it went through its charging cycle (NOCO GENIUS10) in a matter of minutes and settled into MAINTENANCE MODE.
That suggested (to me anyway); that the battery wasn’t really flat - but I left it 24hrs, put it back in car - and everything back to normal.

Next day I tested the battery with a BATTERY TESTER (SOLAR BA7) and TBH, I couldn’t see anything wrong:
  • Lo load voltage was 12.82V
  • The TEST reading was 929 (CCA I guess that’s the units) - it gave a status of GOOD / GREEN.
  • I took a reading at cranking load - voltage dropped to 9.69V.
  • The Charging Voltage at 1,500RPM was 14.32V No Load.
  • The constant At Load reading was between 14 and 14.2V.
Any thoughts / advice on what’s going on here would be greatly appreciated.

All best Ed
MB batteries have 2 year warranty (from memory - might be longer now). Why don't you take the battery back to the dealer that you bought it from, and have them test it, and replace it under warranty if necessary?
Hi - thanks reply.
I could as it’s fairly local - and it’s only six months old
Are you leaning toward a duff battery ?
Hi - thanks reply.
I could as it’s fairly local - and it’s only six months old
Are you leaning toward a duff battery ?

I don't know, but the dealer will need to test the battery in order to decide whether they are replacing it or not.

If it's not the battery, then you'll need to take the car to an automotive electrician to check the alternator and the battery management system, there's only that much you can check at home with DIY tools.
Hi - thanks reply.
I could as it’s fairly local - and it’s only six months old
Are you leaning toward a duff battery ?
Do you not have two batteries?
Do you have a Halfords local to you? They will do a battery and alternator test FOC, have had that a couple of times myself and daughter just had her Citroen checked, you may have to phone and book. Their batteries come with a 5 year warranty - and they had to replace one for me after a few months!
Hi all - thanks for replies.

Re ‘do you not have two batteries’ - if you mean:
  • Do I have the smaller Aux battery under bonnet - no; just the one in the boot on this model.
  • Do I still have the 12 yr old one I removed - no; went to local recycling centre months ago.
And thanks for Halfords tip - I’ll probably stick to MB as they supplied battery.

Giving this a bit more thought - broadly, I’ve got three ‘wear and replace’ components involved here
  1. The battery
  2. The serpentine belt and
  3. The brushes in Voltage Regulator
I can’t find anything wrong with Battery using my simple tests and the Serpentine Belt is in good order.
I’m wondering if changing the VR is worth a punt - and at 90k miles not bad idea anyway.
The Alternator is quite tucked away (can hardly see it!) - does the radiator need to come off ?
Can you change VR in situ ?

Best Ed

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