W203 C180 Kompressor Battery issue

robdx · Apr 23, 2025

Hi all
I am in the process of clearing up a few nagging issues on my beloved old girl, she has just had major surgery to get through the MOT(curse the state of the roads). My biggest nagging issue at the minute is the battery terminals. My battery is running down after 2 days if not used, I do have a spare that I keep fully charged but I would love to solve it propperly. Obviously I am well aware it could be a power drain but my terminals are pretty loose and I have got to a stage where I can't tighten them as they are just rusted solid and the nut is just rounding to the point where I have had to split the nuts and replace the bolts, I got them out cleaned the terminals however the "Square" end of the bolts i procured from a local scrappers (not off a merc btw) are a bit small and can spin, but between me and my mate we managed to get them tight on.
Before I got the old bolts out the terminals were very loose so I am wondering if this could have caused a discharge and not getting enough charge back in from the alternator. I have had both baterries and alternator checked and both test A1. I would like to get a couple of better bolts with a bigger square end, am I better going back to a scrappers or is there anywhere I can get a pair? Looking at the terminals it seems the square end is supposed to be bigger so it cant spin on tightening. I just want to eliminate the possibility of loose terminals being the cause of the drain before chasing other options. I dont have memory seats, my alarm sounder does not work so thats a possibility, I also have an aftermarket head unit installed which could also be the cause but thats been in 2.5 years and the drain is recent.
Could anyone advise me please

DesireeE · Apr 24, 2025

robdx said:
Hi all
I am in the process of clearing up a few nagging issues on my beloved old girl, she has just had major surgery to get through the MOT(curse the state of the roads). My biggest nagging issue at the minute is the battery terminals. My battery is running down after 2 days if not used, I do have a spare that I keep fully charged but I would love to solve it propperly. Obviously I am well aware it could be a power drain but my terminals are pretty loose and I have got to a stage where I can't tighten them as they are just rusted solid and the nut is just rounding to the point where I have had to split the nuts and replace the bolts, I got them out cleaned the terminals however the "Square" end of the bolts i procured from a local scrappers (not off a merc btw) are a bit small and can spin, but between me and my mate we managed to get them tight on.
Before I got the old bolts out the terminals were very loose so I am wondering if this could have caused a discharge and not getting enough charge back in from the alternator. I have had both baterries and alternator checked and both test A1. I would like to get a couple of better bolts with a bigger square end, am I better going back to a scrappers or is there anywhere I can get a pair? Looking at the terminals it seems the square end is supposed to be bigger so it cant spin on tightening. I just want to eliminate the possibility of loose terminals being the cause of the drain before chasing other options. I dont have memory seats, my alarm sounder does not work so thats a possibility, I also have an aftermarket head unit installed which could also be the cause but thats been in 2.5 years and the drain is recent.
Could anyone advise me please

Hey there Rob, sorry to hear of your woes, and I am no expert on these things, but I will chuck my two penneth in the mix, even if I am way off base, just in case something I say gives you a little glimmer of help, but I am definitely not trying to teach granny to suck eggs here, so no offence meant.
First off then I asked 'Copilot' the question and here's the reply:

Then I wanted to know how to check if there was a problem and how I could go about changing the faulty cables so posed the questions and the answers Copilot came up with were pretty straight forward ...

I like the sound of No.4 ^^^

Now a quick YT video to show you how it's done, just like that ...

DesireeE · Apr 24, 2025

That should be the answer to your theory of the loose connection and lack of charge getting to the battery hopefully, so my next line of though relates to the battery itself. You say you have had it tested and it is A1, not wishing to question this but just some thoughts on the subject as sometimes an A1 battery on the one hand may not be so on the other and what I'm thinking of is having done the drop test. This just means taking the voltage reading with the engine ticking over and nothing switched on, then compare that reading to one taken when you turn the lights on making a demand for power from the battery you will see the voltage 'drops'.

My concern is that your battery(s) only hold a charge for 2 days, which is odd if they are fully charged to start out with, and are capable of holding that charge, my suspicion is that they are not, although I could be completely wrong here. It is my understanding that once a battery has gone below a certain charge, it incapable of being salvaged - it is for all intents and purposes dead and the time has come to get a new one.

The figures I am talking about go something like this although reading various bit 'n' bobs, will give you different answers of course, this gives you an idea though all the same:

12.6V - 12.7V --> fully charged and in great condition

12.4V - 12.6V --> Charge okay but some degradation has occurred

12.2V --> this is at ~ 50% charged and the battery needs to be recharged

10.5V - 11.0V --> Severely discharged with a likely bad cell

Below 10.5V --> probably beyond recovery and the battery is defunct

Funny enough temperature can affect batteries too, that's why EVs (electric vehicles) suffer range changes in different weather conditions and climates.

As most of my cars see very little annual mileage, I have them on a CTEK battery charger when not in use, that way I know the battery is tip-top and I will get the most life out of them that I can. I was never a boy scout but am usually prepared dib-dib

robdx · Apr 25, 2025

DesireeE said:
That should be the answer to your theory of the loose connection and lack of charge getting to the battery hopefully, so my next line of though relates to the battery itself. You say you have had it tested and it is A1, not wishing to question this but just some thoughts on the subject as sometimes an A1 battery on the one hand may not be so on the other and what I'm thinking of is having done the drop test. This just means taking the voltage reading with the engine ticking over and nothing switched on, then compare that reading to one taken when you turn the lights on making a demand for power from the battery you will see the voltage 'drops'.

My concern is that your battery(s) only hold a charge for 2 days, which is odd if they are fully charged to start out with, and are capable of holding that charge, my suspicion is that they are not, although I could be completely wrong here. It is my understanding that once a battery has gone below a certain charge, it incapable of being salvaged - it is for all intents and purposes dead and the time has come to get a new one.

The figures I am talking about go something like this although reading various bit 'n' bobs, will give you different answers of course, this gives you an idea though all the same:

12.6V - 12.7V --> fully charged and in great condition

12.4V - 12.6V --> Charge okay but some degradation has occurred

12.2V --> this is at ~ 50% charged and the battery needs to be recharged

10.5V - 11.0V --> Severely discharged with a likely bad cell

Below 10.5V --> probably beyond recovery and the battery is defunct

Funny enough temperature can affect batteries too, that's why EVs (electric vehicles) suffer range changes in different weather conditions and climates.

View attachment 170824

As most of my cars see very little annual mileage, I have them on a CTEK battery charger when not in use, that way I know the battery is tip-top and I will get the most life out of them that I can. I was never a boy scout but am usually prepared dib-dib

I have 2 baterries, both have run down in the car however both will recharge and hold that charge.
Battery 1 is around 4 years old and it went flat around October 24, breakdown came out and got it going, after a 7-8 mile run I took it to a garage who tested battery and alternator A1, however it flattened again a few weeks later (after 3 days of no use) so this time I assumed it was on its way out and bought a new one...Battery 2. My mate charged up battery 1 to check if it would hold charge. After 5 weeks in his garage it still read 12.7 v
Battery 2 is practically new but has still run flat after 2-3 days of no use, but does charge up ok.
Current state of play is Battery 1 is on the car, with tightened terminals and started ok yesterday but did sound a little weak when starting, battery 2 is fully charged and sat behing the passenger seat just in case. From that I think there is a drain which i'm hoping to test at some point today

DesireeE · Apr 25, 2025

robdx said:
I have 2 baterries, both have run down in the car however both will recharge and hold that charge.
Battery 1 is around 4 years old and it went flat around October 24, breakdown came out and got it going, after a 7-8 mile run I took it to a garage who tested battery and alternator A1, however it flattened again a few weeks later (after 3 days of no use) so this time I assumed it was on its way out and bought a new one...Battery 2. My mate charged up battery 1 to check if it would hold charge. After 5 weeks in his garage it still read 12.7 v
Battery 2 is practically new but has still run flat after 2-3 days of no use, but does charge up ok.
Current state of play is Battery 1 is on the car, with tightened terminals and started ok yesterday but did sound a little weak when starting, battery 2 is fully charged and sat behing the passenger seat just in case. From that I think there is a drain which i'm hoping to test at some point today

Good luck with the test, and have a go at the 'drop test' too, as that will give you a better idea of the actual state of play of battery 1 the newest battery.

I found these for you which you might find interesting/helpful and the relevant bit with the first clip only takes a minute or two, so they are all pretty short:

W203 C180 Kompressor Battery issue

robdx

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