Confusing electrics issue

[EJD]

I have an intermittent issue that is confusing.
I have a 2010 CLC 200cdi and had the battery replaced due to this issue a few weeks ago as the reader reported lots of under voltage errors and the battery was as old as the hills.
unfortunately this has not cured the overall issue but has resolved the undervoltage.
It manifests in several ways.
The first is that when I try to start the car, on about 15% of attempts, it kicks the starter motor over for .5 - 1 revolution then just goes dead, no lights on the daash nothing. If I try to restart the car it occasionally does the same aain but usually starts up fine.
Sometimes when it starts, when I put it into drive or reverse it cuts out and I have to restart it.
On three occasions, it has cut out wjile pulling away from standstill.
yesterday the big red battery appeared on the dash as I was driving up the street. I turned around and went home andwhen I turned it off and restarted there was no red battery light.
This morning I have put my multimeter on the battery.
12.6 volts from overnight cold.
When I turn the ignition to get the dials to fire, it drops to about 11.4 - 11.6. I assume this is normal due to load of heaters etc.
The car failed to start twice when monitoring this.
It started fine on multiple occasions and once running the battery intially showed 14.2v charging then after a few seconds it rose to 14.4 - 14.6 - no real variation when revved.
I checked the battery contacts and earth lead and they are secure.
I can't see how its the regulator on the alternator as the fault occurs before the engine is running even though a couple of the symptoms point towards it and I am struggling to find a place to start diagnosing this.
Are there any relays or common wirng / fuse issues that may cause this?
The reader shows there are no electrical errors reported now but I do have an O2 sensor fail but that should not cause this issue.
Anyone seen anything similar or have any ideas?

I don't want to spend a fortune on the car as we are emigrating in 4 months and just need it to be reliable enough to use and sell.

 

[Petrol Pete]

What battery was fitted and by whom ?

 

[ChrisPDuck]

Could it be the EIS module at fault? That's the module that the key slots into.

 

[markjay]

Your intermittent problems won't be related to low voltage or failed battery, but to a failing electronic component, one candidate is the EIS module as ChrisPDuck suggested.

You'll need to take the car to an independent specialist who will scan for fault codes using MB STAR diagnostic computer which will hopefully help pinpoint the failing component.

 

[richard]

I would check the battery voltage (with everything on) across the battery terminals, and then also between the positive terminal on the battery and the ground jump point on the body - this checks the ground connection from the battery to the body - should be very little different between the two readings. Easy check before moving onto EIS etc which are all expensive.

R