# Replacing/charging the car battery



## captainhero17 (Apr 10, 2018)

The winter is creeping up on us.
So I was thinking about my cars battery. Its the original one from 2015 (the same year of my car model).

Can you:
1. Replace the car battery yourself (in the case of it being dead or too old)?

2. Can you disconnect the current car battery and charge it with your car battery charger and put it back?


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## phazer (Apr 2, 2018)

You'll need a diag tool like VCDS to "tell" the car it has a new battery if you do swap it yourself.

I wouldn't have thought charging off the car would be a good idea for the same reasons as above - the car monitors the battery, its charge state and so on.


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## Edinburra (Aug 19, 2016)

captainhero17 said:


> The winter is creeping up on us.
> So I was thinking about my cars battery. Its the original one from 2015 (the same year of my car model).
> 
> Can you:
> ...


 As to replacement, only if you are experiencing problems.

No need to disconnect the battery to charge it. Get yourself a CTEK fully automatic battery charger, that will charge and condition your battery. It'll cost around £70.00 on Amazon.


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## captainhero17 (Apr 10, 2018)

phazer said:


> You'll need a diag tool like VCDS to "tell" the car it has a new battery if you do swap it yourself.
> 
> I wouldn't have thought charging off the car would be a good idea for the same reasons as above - the car monitors the battery, its charge state and so on.


So one day when I get inside my car in the winter morning to go to work and the car wont start I have to call a tow service to schlep me to Audi service where they will scalp me with a 30% mark-up?

What idiot came up with this design?!!! :twisted:

*P.s- Edinburra* suggested a charger that can charge the battery while its still connected to the car. Is that recommended? I read that this can give some problems to the MMI system and other electronic parts.


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## Hoggy (May 8, 2002)

captainhero17 said:


> *P.s- Edinburra* suggested a charger that can charge the battery while its still connected to the car. Is that recommended? I read that this can give some problems to the MMI system and other electronic parts.


Hi, A Ctek mxs 3.8 will charge/maintain any battery on or off the car.

Example.
https://www.ebay.co.uk/p/CTEK-MXS-3-8-1 ... 178&chn=ps

Hoggy.


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## phazer (Apr 2, 2018)

captainhero17 said:


> phazer said:
> 
> 
> > You'll need a diag tool like VCDS to "tell" the car it has a new battery if you do swap it yourself.
> ...


It's to do with the way these batteries are charged and the monitoring loops the car has. Same reason you can't jump them like older cars - there's separate connections on the bulkhead for that. If you're going to use a charger check the manual to see if you need to use the jump points or can connect direct to battery.


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## Edinburra (Aug 19, 2016)

Hoggy said:


> captainhero17 said:
> 
> 
> > *P.s- Edinburra* suggested a charger that can charge the battery while its still connected to the car. Is that recommended? I read that this can give some problems to the MMI system and other electronic parts.
> ...


Thank you for your reply. I've used this bit of kit with various cars over the last 10 years with excellent results. It's money well spent.


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## brittan (May 18, 2007)

Edinburra said:


> No need to disconnect the battery to charge it. Get yourself a CTEK fully automatic battery charger, that will charge and condition your battery. It'll cost around £70.00 on Amazon.


CTEK chargers are what I use and have done for some years now. No issues with doing so direct onto the battery on the Mk3.

If you have a walk around any Audi showroom, and I suspect other VAG showrooms too, you will see all the cars in said showroom connected to CTEK chargers.


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## captainhero17 (Apr 10, 2018)

OK I see now what product I have to have. This thread was more about what if/prevention. Rather than having a problem right now. But you know, better to ask now then frantically trying to get an answer when it happens. :lol:

I will take a look at some chargers out there. Dont think that CTEK delivers to my country. 
I think that BOSCH does them as well. I just need to make sure that the charger is compatible with Start/Stop battery system?


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## ZephyR2 (Feb 20, 2013)

I got the CTEK MXS 5.0 (just a bit more power than the 3.6) for about £60 from Amazon. Check Amazon where you live, I'd have thought they'd offer it there too.
I've used mine on my Mk2 and the Mk3 TT without any problems. As brittan said they are widely used in showrooms. I had my Mk3 laid up for 4+ weeks with the CTEK connected permanently.
They are intelligent chargers designed for modern cars and their batteries. If you think you could be using it frequently you get connectors which attach to the charging points under the bonnet so that re-connection of the CTEK is just a matter of plugging it in to a socket each time.


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## macaddict111 (Jun 13, 2018)

phazer said:


> captainhero17 said:
> 
> 
> > phazer said:
> ...


The computer is basically just keeping track of "amps in, amps out", which is reset when you put in a new battery. Older cars would simply put the alternator at 14 volts and the battery would take all the current it wants, sometimes too much for the alternator which would get hot and cause a high or rough idle, especially after a cold start when the engine the engine needs a big power sap least. Now the ECM controls how much power the alternator picks up, and most of the charging of the battery happens when you lift off the throttle and coast (hence little green battery section on MPG gauge). This helps save fuel and increase peak power, as the alternator doesn't drain as much when it shouldn't.

It's also important for the afterrun cooling program (coolant pump and fans), as the computer needs to know how much reserve power it can take from the battery after shutdown before it affects starting the next time.


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## BauhauTTS (Jan 8, 2017)

macaddict111 said:


> It's to do with the way these batteries are charged and the monitoring loops the car has. Same reason you can't jump them like older cars - there's separate connections on the bulkhead for that. If you're going to use a charger check the manual to see if you need to use the jump points or can connect direct to battery.


The computer is basically just keeping track of "amps in, amps out", which is reset when you put in a new battery. Older cars would simply put the alternator at 14 volts and the battery would take all the current it wants, sometimes too much for the alternator which would get hot and cause a high or rough idle, especially after a cold start when the engine the engine needs a big power sap least. Now the ECM controls how much power the alternator picks up, and most of the charging of the battery happens when you lift off the throttle and coast (hence little green battery section on MPG gauge). This helps save fuel and increase peak power, as the alternator doesn't drain as much when it shouldn't.

It's also important for the afterrun cooling program (coolant pump and fans), as the computer needs to know how much reserve power it can take from the battery after shutdown before it affects starting the next time.[/quote][/quote]

Thanks for this explanation - very interesting.


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## kevin#34 (Jan 8, 2019)

reopening this thread again, to improve the *what if/prevention* matter&#8230;
regarding periodical battery charging, I followed what owner's manual says (don't connect the charger directly to the battery, instead use the dedicated terminals), while for what concerning battery replacement, I found out that the new battery must be a BEM type and must be properly coded:


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## captainhero17 (Apr 10, 2018)

kevin#34 said:


> reopening this thread again, to improve the *what if/prevention* matter&#8230;
> regarding periodical battery charging, I followed what owner's manual says (don't connect the charger directly to the battery, instead use the dedicated terminals), while for what concerning battery replacement, I found out that the new battery must be a BEM type and must be properly coded:


Nice update.
Still pisses me off that I have to use a service to replace my battery. My old Fiat Punto is a freaking god sent vs this car.

For the battery replacement, I only heard that you have to make sure that the battery is the one designed for start stop cars. But then again since you are going to take it to the specialist let them think for ya as well. :lol:


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## kevin#34 (Jan 8, 2019)

buy a VCDS, and you will be able to code a new battery for yourself (plus dozen of other things!).
Also, you could save money by buying a battery without BEM (providing it has the correct spec) and code it as if was a BEM type (just incrementing the last battery serial number figure by 1).


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## captainhero17 (Apr 10, 2018)

kevin#34 said:


> buy a VCDS, and you will be able to code a new battery for yourself (plus dozen of other things!).
> Also, you could save money by buying a battery without BEM (providing it has the correct spec) and code it as if was a BEM type (just incrementing the last battery serial number figure by 1).


VCDS is expensive and I already have pro OBDeleven. And even that thing is too much for me. I already hang out on this forum more than I need to. I see what buying VCDS does to people who already are not experts in it :lol: :lol: :lol:

But I will remember the pointeres about BEM battery once I really need to change it. For now its bellow 12V (11.6 acc to OBDeleven) and it will drop more if its not driven for longer periods. But its already cold outside so no wonder the battery is struggling a bit


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## kevin#34 (Jan 8, 2019)

well, VCDS clones are at around 20/25 pounds on aliexpress, should you convert yourself in a VCDS-fan.... :lol:


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