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Discussion Starter · #1 ·
Charging my Yeti’s battery
My Yeti is SE L TSI (110HP) DSG stop-start with an AGM 69Ah battery with negative earth.

Mains charging
I tried using my very old trickle charger. Obviously it has no AGM setting. It did not seem to do much. I hope that I have not upset anything. The forum seems to advise a CTEK MXS 5.0 , so I purchased one. It has a special setting for AGM batteries. However, after leaving it charging my Yeti battery for 3 days it was still at stage 6, and the battery not fully charged nor floated, as in stages 7 and 8. I put the charger leads directly on to the two battery terminals. However, I read on this forum that because of the battery monitor this is not good. Hopefully there is no long-term damage. I tried using the post immediately to the near-side of the battery, thinking that it was a frame terminal, which this forum seemed to recommend for use rather than the battery negative. However, when I did this the charger stopped working and the flashing power light indicated that the terminals were not connected.

My Skoda main dealer advises against mains charging via the 12V front socket, but he did not explain why.

(When using jump leads to start an engine with a flat battery by using another battery, I understand that the procedure is to attach the negative lead to the car’s frame rather than to the dead battery’s negative terminal. But of course this is for a completely different reason, that of avoiding a spark in an area of hydrogen gas.)

I tested the battery’s health with my electronic battery tester, and also had it tested by an auto-electrics professional. Both results were about 75% good.

Soon after running my Yeti on a trip, or after the battery being charged, the battery’s voltage soon drops to about 12.4 V at the 12v socket between the two front seats. This seems to be the same voltage as at the battery itself. If my battery was a normal flooded lead-acid battery I would expect this voltage to be higher.

The engine always starts very quickly, and I have never had any battery problems, except when I left the driver’s door open for an afternoon and drained the battery to zero, before immediately re-charging it.

Solar cell charging
Because I intend to leave the car parked for months at a time I have purchased a 10W solar charger. Obviously solar cells do not have an AGM setting. I understand that to avoid the solar cell cooking the battery I should follow the 10% rule: the wattage of the solar cell should be less than 10% of the Ah of the battery. Clearly 10(W) is greater than 10% of 69(Ah). However, I believe that when the engine is switched off and the car locked, there is a continuous drain from the Yeti’s battery (I do not know the mA involved) in order to monitor many things, including monitoring the battery perhaps, but certainly including listening for the wireless “open-door” signal. I am slightly concerned about using this 12V socket in case it interferes with the battery management system.

I asked at a Skoda garage. They said that they could not recommend using the internal 12V sockets for charging the car’s battery using a solar cell. I presume that the socket is protected by a fuse of a certain amperage and that there are no other loads on that circuit. I have used this method for maintaining (rather than charging) a car’s battery on less sophisticated cars previously. However this car also has, I believe, a battery monitor.

The above contains no explicit questions. However there are many implied questions. I would be most grateful to hear the experience and opinions of Yeti Club members. Thanks.
 

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I have never had any battery problems, except when I left the driver’s door open for an afternoon and drained the battery to zero, before immediately re-charging it.
That should not cause a problem because the interior lights go off after a period of time as does the radio to stop the battery from being unable to start the car..
 

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CTEK MSX5.0 will be fine on the 12V sockets.

CTEK's adaptor is fused lower than the cars internal fusing and is safe to use with the 5.0 or 7.0 CTEK's but not the 10 as the current is too high.

Skoda's guidance is just a catchall safety guidance for people who would stick a large charger on with sustained high current.

My Yeti sits all week most weeks and sometimes for a couple of weeks. I use the CTEK 12V adaptor and plug it in the rear 12V socket and close the rear hatch. Leave it for weeks.

As for why your battery is going flat and the CTEK never floats. It's either battery (Even though you have tested it) or a current draw on the car.
 

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I don't have stop start but have used the boot power socket as a charging point for years. I use a Ctek charger, and it coped with a prolonged lay up after a knee replacement and throughout the lockdown etc.
 

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Lots of good advice above. Some extra thoughts:
A Ctek charger plugged into either power socket will work perfectly well on a stop/start equipped system too.

The battery management module has resistance and that is how the ecu can monitor voltage and current flow. If you are charging direct onto the battery’s negative post, do not be surprised if the charger objects. AGM batteries have lower internal resistance than flooded lead acid types and are less tolerant to overcharging, which could lead to thermal runaway. This is the reason why the battery management module also monitors temperature.

A 10W solar panel will only give that amount of power at lunchtime in Barbados (especially if it is a cheap Chinese piece of kit). This means that the most current you would expect to get out of it would be lets say 10/14 amps or 700mA. Most of the time it will be putting much less than half an amp into the battery and that will be for less than the daylight hours. This will be just about enough to make up for the losses that the various bits are drawing while the car is unattended. I really would not get excited about anything frying.
 

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Discussion Starter · #8 ·
The post to the nearside of the battery is where the battery's negative wire attached to the chassis. I thought it would be a good electrical earth connection, but it is so well painted that it is not a reliable earth. Maybe I just scrape off the paint? Which bit of the engine frame do people use as a reliable battery earth, eg when mains charging ?

Thanks to all those who have responded.
 

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The post shouldn’t have paint on it. You are looking at the post which is mounted on the bulkhead to the right and rear of the battery?
 

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The post to the nearside of the battery is where the battery's negative wire attached to the chassis. I thought it would be a good electrical earth connection, but it is so well painted that it is not a reliable earth.
This is where you should connect the charging negative.
Automotive tire Motor vehicle Machine Auto part Automotive design
 

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I don't have stop start but have used the boot power socket as a charging point for years.
I do have start/stop and have used the boot power socket as the charging point for my CTEK for over 3 years without issue.

Not much else I can add to all the above posts except that the CTEK takes a long time to get to Stage 8 as the charger remains at Stage 7 for 10 days.
 

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From the comments made by the OP I'm beginning to wonder whether he might have cooked to voltage controller by his totally incorrect method of connecting the battery. Why don't people RTFM!!!
 
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Discussion Starter · #13 ·
Why is it better to connect the negative charger lead to the frame rather than to the battery's negative terminal ? They are both at the same electrical potential.
The post shouldn’t have paint on it. You are looking at the post which is mounted on the bulkhead to the right and rear of the battery?
Yes, the post in the engine bay as in the #10 post in this forum thread.
 

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Read my post #5 again. If that doesn’t make sense, perhaps you should just accept the advice that various knowledgeable people on here have given you?
 

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It looks like you will have to scrape the paint off. I would not get too hung up on getting a plastic cap.
 

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Discussion Starter · #17 ·
From the comments made by the OP I'm beginning to wonder whether he might have cooked to voltage controller by his totally incorrect method of connecting the battery. Why don't people RTFM!!!
I did connect the negative terminal to the post, but (as I said) the charger would not charge because it said there was no connection. Later I discovered that it was quite correct, due to the post being painted, there was no proper electrical connection.

I was be most grateful if you could explain the reasoning for using the chassis rather than the negative battery terminal. I had thought (as I said) it was to remove the connection way from the area of possibly hydrogen gas in case of a spark. However, this post is very close to the battery.

Would you be able to explain how I might have damage the "voltage controller" when charging the battery by using the battery's negative terminal rather than something that is directly connected to it and at the same potential ?
 

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I mentioned in the second paragraph of #5 that the battery management module has resistance. This is connected between the battery negative terminal and the earth post. Therefore the two can’t be at exactly the same potential because there will be a voltage drop across the battery management module.

If you bear in mind that the charging system and the remainder of the equipment and the two sockets are all connected to the earth post and not the negative terminal, why do you think your battery charger should be?

I am happy to start going into heavy detail as to why, but I fear you may not understand that, so please just accept everyone’s advice.

Once you have properly cleaned the earth post, try the charger again.
 

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Discussion Starter · #19 ·
I do have start/stop and have used the boot power socket as the charging point for my CTEK for over 3 years without issue.

Not much else I can add to all the above posts except that the CTEK takes a long time to get to Stage 8 as the charger remains at Stage 7 for 10 days.
I said that CTEK had reached stage 6. That was not true it had probably reached stage 7, but because the light is green not orange (which was what I was expecting), and because green does not show up very well, especially in bright sunlight, I did not see that stage 7 (fully charged) it was illuminated.

I am very please to learn that it is quite normal to take possibly 10 days on charge to get to stage 8, pulse charging. Many thanks.
 

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Discussion Starter · #20 ·
I mentioned in the second paragraph of #5 that the battery management module has resistance. This is connected between the battery negative terminal and the earth post. Therefore the two can’t be at exactly the same potential because there will be a voltage drop across the battery management module.

If you bear in mind that the charging system and the remainder of the equipment and the two sockets are all connected to the earth post and not the negative terminal, why do you think your battery charger should be?

I am happy to start going into heavy detail as to why, but I fear you may not understand that, so please just accept everyone’s advice.

Once you have properly cleaned the earth post, try the charger again.
My previous car is 28 years old, so I am a bit of a dinosaur. I had no idea that cars had battery monitors, and certainly no information about its location. I can find nothing in the Yeti manual. Thank you for your advise as to its location. I now see the necessity of using the earthing post, which I will unpainted. The Yeti manual also makes no mention of where to connect the negative terminal when charging. Many thanks.
 
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