Is it another defective MB Battery or has the CTEK CT 5 decided to malfunction?

[LostKiwi]

Given chargers only operate at 10A or less it should make no difference. If an earth point is bad it will show far more under cranking current.

 

[Botus]

When no current is flowing, both ends of the wire are at the same potential (voltage).
When current flows through a wire it has a voltage drop caused by the wires resistance, connections also cause resistance.
I'm not convinced a direct connection for charging is any worse than the earth pin.
If there's a poor connection at a battery terminal or earth pin due to corrosion, the charger would work best when connected directly to the battery.
The connection would need to be rectified but direct connection would ensure the charger is not blamed if the body contact was poor for any reason
I'm happy to be told I'm wrong if the charger does read the battery charge state and any vehicle sapping losses better from a point further away.

but cars do eat loads of power when off... that's why they play up so much if you don't drive them. don't drive the w221 for 3 weeks and the battery will happily take 4 amps for 24 hours non stop

both my omegas (with new batteries and never having an issue if you drove then regularly) would be dead if left. The first with a bigger tractor battery would be dead at 3 weeks the later 3 ltr petrol one regularly needed assistance to start up if left for 2 weeks

many modern cars (including Audi BM and Merc) have a separate earth post that the user manual say to use to connect up with

and the last point about connecting up the charger... the late great television agreed this was the right way

 

[Submariner1]

don't connect to BOTH battery terminals

one to + on the battery and the other to an earth on the vehicle

Negative goes to the (brass top hat) Vehicle body earth. Main dealer showed me where and explained its vital to do that in the C216, as they have a Battery Cotrol Module, and you can wreck them .... pretty expensive item apparently, and if you leave it broken it can screw up your alternator .

 

[Submariner1]

I always connect to the earth bolt because it's an easy connection but direct to the battery is as good if not better because it's the battery that he is charging, so a direct connection can't be worse than charging through the negative cable from an earth point.
I think you might be thinking of jump starting which is when the negative should be connected to the earth of the vehicle to get the path of least resistance.

Sorry but you are definitely wrong on the C216.
Positive to Battery pos, and negative to brass top hat vehicle earthing point.
At best you will mess up the charging from the alternator, at worst you will kill the BCM !

 

[Submariner1]

allegedly ...if the car is pulling current out of the battery, by connecting ones charger not to the battery post, the charger gets a better reading of what's going on

In addition the later “ein batterie” model had a sophisticated BCM ... erog if the battery voltage is on the low side for the first part of the journey the alternator output is boosted to 14.8v after a reasonable distance it is told to crank it down.
Its a feature to help short journey users.
If you look closely you will see a thin wire from the negative “block thing”to the positive terminal.

The top technical guy at my dealers explained it all to me.
Ignore this on a C216 Post 2009 and you do so at your peril,.. the BCM cost £600+ and refitting the moulded in heavy negative cables are a Mare ££££

 

[Submariner1]

Update
GREAT SUPPORT FROM CTEK UK

THE REPLACEMENT CT5 STOP START ARRIVED YESTERDAY.

All good, now charges up to 14.6V and 3.6A ( before 12.9V and 3.1A)
It also doesnt go into “Care mode at 12.9V after 3 hours, but stays charging @ 14.2V. For at least 8 hours.
It also doesn't get hot, just luke warm.

Once care mode was achieved and disconnected charger. Left overnight the batteriy showed 12.7V not the recent 12.3V.
So seems the charging issue is sorted, other than this battery is crap!

Btw Ctek have a 5 year warranty

 

[L John]

Sorry but you are definitely wrong on the C216.
Positive to Battery pos, and negative to brass top hat vehicle earthing point.
At best you will mess up the charging from the alternator, at worst you will kill the BCM !

Are you saying connecting a smart charger direct to the battery instead of the earth post can do all that damage?
Can't see it myself mate.

 

[Submariner1]

Are you saying connecting a smart charger direct to the battery instead of the earth post can do all that damage?
Can't see it myself mate.

Well probably the best Merc mechanic showed me the MB advisory, and explained why. Since my first Merc back in 1989 if ever I had a problem he has always looked at it and pronounced the right fix ... first time!
When I had a massive fight with MB demanding a new £80K SL be replaced. MB told me to F off, he explained what was wrong .. and MB UK asked who told me that. When I told them who, this manager said “well he is probably the best Mercedes Diagnostic Technician in the UK. If he confirms what you told me we will immediately replace the car” ... and they did!

They also say you should pull out the KLG plug to protect the ECU and other modules.
Hey what do I know ... I just assume there are some clever people in Mercedes who make these recommendations for a reason.
But if you can afford to pop a BCM and shell out £800 to replace it be my guest!

Ask yourself why do they have a vehicle ground point?

Note on the code 809, its not the same battery controller as the one on previous models.

Obviously if the battery is disconnected no probs sticking it on both terminals.

 

[L John]

Ask yourself why do they have a vehicle ground point?

It's for jump starting, a body earth should always be used on any car for jump starting.

 

[Submariner1]

A

It's for jump starting, a body earth should always be used on any car for jump starting.

And for charging .. read the MB Charger instructions.
BTW Ctek make the MB charger.

Obviously I cant convince you. All I would say is if you have a Code 809 or later C216 ... go and ask your Dealer.
Hey its your car .. you can do what you like.

 

[L John]

As I said earlier, I would always use the earth post anyway because it's handy.
Not convinced about any damage to the alternator or BCM by connecting a smart charger direct to the battery though, so I would be happy to do it either way.

 

[dreadlockdw]

I'm a bit confused by the above discussion as CTEK make quick connectors which permanently connect to the positive and negative car battery terminals to allow speedy connection of their chargers. I've been using this method for over 4 years.

 

[alexanderfoti]

A

And for charging .. read the MB Charger instructions.
BTW Ctek make the MB charger.

Obviously I cant convince you. All I would say is if you have a Code 809 or later C216 ... go and ask your Dealer.
Hey its your car .. you can do what you like.

On the 216/221 with 2 batteries and a BCM the negatives are all tied together. The positives are the ones you have to be careful with.

 

[L John]

I'm a bit confused by the above discussion as CTEK make quick connectors which permanently connect to the positive and negative car battery terminals to allow speedy connection of their chargers. I've been using this method for over 4 years.

You've been lucky then
The negative post of the battery and the earth post are connected by one of the the thickest cables you have on the car. The cable has very low resistance due to the many cores in parallel, so the battery post and the earth post are basically the same thing unless high current is flowing such as when jump starting.

One of the reasons for an earth post being away from the battery is to keep sparks away from the gasses given off when lead acid batteries are charging but the earth post is really not far from the battery anyway and valve regulated batteries are safe unless charged incorrectly.
Your charger lead is bolted to the battery and has a quick connector, so you're not making a connection of the charger directly at the battery anyway.

 

[Botus]

I've just written to the manufacturer of both my "decent chargers" I wonder what there response will be:


I have two of your battery chargers. An xxx and an yyy. Both never go above 12.6volts on any battery they are connected to, with any battery type or size, e.g. brand new or older, AGM, Gel or conventional lead acid. I was wondering if this is a feature but then whilst a dealership on 3 Nov 2018 he thought this was clearly a fault and we noticed the packaging for the yyy even shows a picture with working at 14.4volts.

So why have both of mine only got to 12.6volt and then switched to maintenance mode, where it remains and after a few days slides to 12.5 volt and comes back reporting battery strength as “strong” ?

I believe they could be faulty and their use may be damaging my batteries.