New battery, keeps going dead??

[Birdie123]

Hi, So my old battery on by 2007 B Class W245 180Cdi started to give me some issues and I brought a new one but never got round to fitting it, anyway a couple of days later, went to start car, doors opened fine, but it would not start, called RAC, who checked everything said Yes alternator is fine, battery dead, and replaced the battery I had purchased. All good for about 4 weeks, then one morning went to start car and it would not start again, called RAC, who checked everything again, said it was just the battery, that maybe I had been unlucky with the new battery and had been sold a dud one.
As it was under warranty, replaced with a new battery and got my garage to change it over, he also at the same time checked everything including alternator and the new replacement battery and was satisfied all was good, and put on the brand new replacement battery.
now about 4 weeks later, again, went to start car and it will not start, dashboard lights come on as before etc, central locking works as before.
on both occasions that I have replaced with a new battery, there was never any warning lights on the dashboard.
I have read somewhere that the alternators on some Mercedes some sort of smart charge and only certain garages would know how to replace a battery correctly however I would have thought the RAC would know this and my mechanic, who knows his electronic well and has been a mechanic for over 30 years would know this too. I have the RAC report
any ideas welcome please

 

[Stratman]

Are you using the car during these four week periods? How far do you drive it between starts?

 

[Birdie123]

I was using it to get to work, being a key worker in social care and I had driven it some 8 miles the night before it stopped.
I now use my daughters car as she can't go anywhere and actually we have been told to do most of our assessments via phone now but in some cases with very vulnerable I still need to go out, I am in learning disability so most of our clients have a learning disability and several other physical serious health issues and without support, at least 90% would struggle to meet daily needs. If things get worse, with more staff isolating, I will be asked to go back out again regularly

 

[Stratman]

Lots of short journeys will eventually lead to a flat battery, as will leaving it standing for an extended period. How often do you use the car, and how far is each journey? How long do you leave it unused?

 

[Birdie123]

I was using the car daily up until a week ago, the battery issue started in January when the first new battery was changed and then replaced again in Feb, my driving habits have not changed so it is very unlikely it has anything to do with this, obviously a new battery is lasting about a month, so there is some sort of very slow battery drain that is happening.

 

[Stratman]

When you try to start it what happens? Does it crank at all? Do the dash lights dim? Any other symptoms?

 

[Petrol Pete]

OP , remember . for some reason that no one can yet explain , if you leave a Mercedes Benz standing for more than 4 weeks it's whole world comes to an end. after that magical time it ceases to be a mode of transport and morphs into a unmovable Menhir that only money can make mobile again...

Sorry, it's late and the Cynic in me has taken over. Welcome to the forum and good luck getting a sensible answer on your battery problems.

 

[grober]

Even with a slow battery drain, with regular use the alternator should easily top up a new battery after a few miles of running provided the charge output regulator is working OK. TWO possibilities 1 either the altenator is not charging adequately 2 there's a parasitic drain which is either permanent or intermittant. Glow plugs/ controllers are a favorite. Dodgy engine earth straps another [ needed to complete that charging circuit ]

 

[Birdie123]

So I went to check the car again today, to answer the query "do the dash lights dim?" and the car doors will not open at all with the fob, so looks the battery is now completely drained.
I looked up the RAC report from Feb, a week or so after which the battery was replaced the second time, the RAC reports informs replace battery due to poor cold cranking amps, this was a new battery so thinking I had been sold a dud, I got it replaced under warranty and put the second new battery into the car, it's this second battery that has now failed. The RAC report also informs:
Alternator voltage (loaded) 14.13 volts (voltage output of alternator during the test with lights and heated rear screen on)
Alternator Current (loaded) 40.1amps (current consumed with system under load)
Not sure what to do now?
Next week, I will probably need the car as the social care situation is looking bad, there will be many hospital discharges for whom a social care package will need to be assessed and commissioned asap to free up much needed hospital beds for expected influx Covid patients, the only positive is I will probably still have access to my daughter's car, as she is not likely to be going anywhere as her school only needs a limited number of teachers and she is not likely to be called up

 

[Dodipops]

You’ll need to get the battery fully charged, then check the drain on the battery with an AMP clamp.
Once you know if it has a drain then you start pulling fuses until it stops.

I recently fixed one for someone else, that turned out to be a faulty microphone for the telephone system, they never used it so I just unplugged the microphone.

Could be plenty other possibilities though.

 

[wongl]

I have read somewhere that the alternators on some Mercedes some sort of smart charge and only certain garages would know how to replace a battery correctly however I would have thought the RAC would know this and my mechanic, who knows his electronic well and has been a mechanic for over 30 years would know this too. I have the RAC report
any ideas welcome please

The W245 does not have smart charging, and replacing a battery in the W245 is a pretty standard procedure requiring the auto windows to be reset and turning the steering from lock to lock.

I am interested to find out more about your replacement battery. What make is it, what capacity and where did you buy it from?

 

[Deleted member 149005]

Maybe an electrical circuit remains open, despite the ignition off, draining the battery?

 

[Bellow]

If you have a battery charger and are able to remove the battery yourself (or disconnect and use charger in situ) disconnect battery, charge, leave disconnected until car is needed. If it starts when reconnected, then the battery is fine and parasitic drain the problem. At your destination it will be safer to disconnect the battery so that it doesn't drain down before you are ready to leave. When disconnecting, remove NEGATIVE terminal. If removing battery disconnect negative first and reconnect it last (safety).

Then, you have to trace the source of the drain. I currently have this problem (see my thread for more info) and it's a PITA!

 

[steveskeggy]

How can the battery be dead if the central locking is working, and the dash lights up as you said in the first post?
How long was the car stood when you tried it again, and it was all dead?
Now, there is a relay for the starter, it looks to be in the fusebox in the passenger footwell, but it may be under the bonnet!
It should be a green relay with the part number 002 542 23 19, make sure you replace it with the exact same relay, as this one has 5 pins instead of the usual 4, and it also has a diode going between two of the pins.
If its not the battery, and all the other circuits are working, then these relays can suffer from weak ****, so if the battery is full, they work, but if the battery is slightly low, they dont, I had the same on my V12 S600, and my current S55 AMG, they both used the same relay, so it looks like this is a common prt for all models.
If you just replace it, and it doesnt cure it, its only a couple of quid, cheaper than replacing the battery anyway.

 

[Stratman]

Just a thought, does your car have memory seats? The control box for these has been known to go faulty and drain the battery. If it does, try disconnecting the plug under the seats.

 

[Bellow]

If you are going to attempt tracking down the source of the drain, you need to start by removing fuses and relays to identify the defective circuit. For this, you need a method of monitoring the current draw. A multi-meter as ammeter is the obvious choice. If you don't have one there are ammeters built into fuses that you slot into where a removed fuse sat and if that circuit is the source of the drain then the current shows. Or there's a test bulb method. See my thread and look for one of Ted's posts for details.
If you can identify the circuit - and whatever it powers isn't crucial to the car's running - then it can be isolated by leaving the fuse out. If it is a necessary circuit, then a repair is obviously in order. In my pursuit of my drain I was urged to isolate the alternator and starter motor leads as the are always live (irrespective of ignition key position) and the alternator especially can cause a drain while still functioning. As the drain occurs without the ignition being on, you only need check without the key in the ignition (or otherwise switched on/energised). This is also safer.

If you are unused to this type of work (but want to try anyway) take great care. A charged battery (your start point) contains a considerable amount of energy. A high current through a thin wire will heat it up very quickly and is both a burn and fire hazard.

 

[Deleted member 149005]

A faulty alarm or mobiliser causing a drain?

 

[Birdie123]

Thankyou guys, certainly some good suggestions there, I have done some research and watched a number of you tube videos but, I think this is beyond my abilities so I am going to get a garage to look at it, if one is open??
My car has no memory seats.
The car was stood for a couple of days before I started it, I think this was last Tuesday when I went out , it was all good, no dashboard lights, no problem starting etc, drove it about 8 miles then instructions came from work to only do home working and only do home visits/care home visits etc if absolutely necessary otherwise all contact by telephone, email etc, Thursday I had need for car, but would not start, doors opened, dashboard lights were on as normal, car was just barley ticking over but not starting, left it and used my daughters car instead, I think then on Friday or sat, went to check the car again and noticed I could not open the doors with the Fob anymore and hence I assumed the battery must have drained all together.
I do not have a battery charger but someone on the street may have one, like everywhere, we have a whatsapp group to look after each other, doing bits of shopping for each other etc so I can ask if someone has a battery charger lend it to me for a while.

 

[Birdie123]

My Original Battery was a Varta 74Ah 680A, I had ordered a DriveTec battery from GSF with specification 77Ah and CCA 780A but infact received a DriveTec 72Ah 650A but the RAC chap who replaced it the first time around, said it was very close to the original Varta so should be OK

 

[Birdie123]

Ho, So I managed to get in the car with my key and with was able to jump start car, after connecting the jump leads, the car would at first not tick over, waited a couple of minutes, tried again and it started up, removed the jump leads and let the car idle for 1 hour and 20 minutes before switch it off. Now 24 hours later, the central locking is responding to the key fob, car started first time, left it to idle again for 1 hour, will check again tomorrow, dashboard lights did not dim or anything unusual.