Battery charging

4.2 V8 32v FSI - 444 bhp
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AndyBrad
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Joined: Fri Jan 20, 2023 1:37 pm

Battery charging

Post by AndyBrad » Wed Feb 01, 2023 12:37 pm

Hello folks,

i use my car very very short trips (school run) with all the electrical gubbins. its going to hammer the battery. as such i would like to charge it while i wash the car at weekends.

does anyone have a recommendation of where i can put a quick disconnect charging point on the car?

johnnydog
3rd Gear
Posts: 481
Joined: Sat Jun 11, 2011 8:24 pm

Re: Battery charging

Post by johnnydog » Sun Feb 05, 2023 1:42 am

I use a Ctek MXS 7.0 smart charger on mine. Any charger used on the B8 RS4 needs to have an AGM charging mode for the battery (which should be an AGM even if a replacement) and be connected directly to the positive terminal under the flap and pop off cover on the scuttle, and the negative post on the nearside suspension turret. However, Ctek provide 'comfort' terminals that can be permanently connected directly to the battery in the boot (even when not in use) with a plug for connecting the plug with the leads from the charger which avoids the use of crocodile clips and the dangers associated with inadvertant sparking, but this is more of an issue with engine bay mounted batteries. I think they do longer leads, but where you have leads coming out of the tailgate or the power cable, it's not as practical as using the front terminals under the bonnet. I connect the leads to the front terminals with crocodile type of clips, place the Ctek charger on the top of the engine, shut the bonnet with just a thin cable exiting by the headlight. I can wash and clean the car whilst charging the battery, which I think is more practical than any leads or cables coming out of the tailgate.
Last edited by johnnydog on Sun Feb 05, 2023 8:26 pm, edited 1 time in total.

MGD
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Joined: Thu Dec 15, 2022 10:57 pm

Re: Battery charging

Post by MGD » Sun Feb 05, 2023 8:50 am

Hi Johnnydog

Any chance you can post a picture identifying the negative post on the suspension turret please?

Thanks

M
Current:
RS4 B8
BMW M2 Competition
BMW i3S

Previous:
Porsche Boxster S 987.2
Mini Cooper SD
BMW M140i
BMW M135i
BMW Z4 3.0si Roadster
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johnnydog
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Re: Battery charging

Post by johnnydog » Sun Feb 05, 2023 7:35 pm

Hope this helps. If you need a clearer picture I'll take a different angle tomorrow.
Screenshot_20230205-183342_Samsung capture.jpg

MGD
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Re: Battery charging

Post by MGD » Sun Feb 05, 2023 9:22 pm

That’s ideal, thanks. I wasn’t sure if it was the bolt just further south of that.
Current:
RS4 B8
BMW M2 Competition
BMW i3S

Previous:
Porsche Boxster S 987.2
Mini Cooper SD
BMW M140i
BMW M135i
BMW Z4 3.0si Roadster
BMW Z3 2.2i

johnnydog
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Joined: Sat Jun 11, 2011 8:24 pm

Re: Battery charging

Post by johnnydog » Sun Feb 05, 2023 10:09 pm

Any substantial earth point will do such as the strut top mount bolts, but you might as well use the specific post intended for the job!

c13dnw
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Joined: Mon Nov 28, 2022 11:18 pm

Re: Battery charging

Post by c13dnw » Sun Feb 05, 2023 10:49 pm

I use the ctek 5.0 and it works well. I do however use it on normal mode as apposed to the AGM mode. I checked the battery in the boot of mine and it doesn't say it's AGM so thought it was safer to go with normal mode. Is that a problem? How can I be sure it's an AGM battery?

johnnydog
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Posts: 481
Joined: Sat Jun 11, 2011 8:24 pm

Re: Battery charging

Post by johnnydog » Sun Feb 05, 2023 11:48 pm

I have a couple of other cars with AGM and EFB batteries, and they state their respective type on the label. AGM generally have a QR type of symbol on this label to assist programming the battery to the car.
I'm sure if you Google the numbers on the label it may state the battery type.
The RS4 had an AGM battery as original spec, but if yours is a standard or EFB battery then it is a replacement albeit of the wrong type for the car.
There are some informative websites that can explain the different fitment types of batteries, possible issues as a result and charging methods etc etc
Incidentally, EFB batteries can be charged as a wet (standard) battery, but AGM batteries have to be charged on the AGM setting.

AndyBrad
1st Gear
Posts: 88
Joined: Fri Jan 20, 2023 1:37 pm

Re: Battery charging

Post by AndyBrad » Mon Feb 06, 2023 10:12 am

thanks for all the information chaps.
is there any battery management system on these cars? i know on bmw you cant connect directly to the battery terminals as this confuses the BMS and shortens battery life

c13dnw
Neutral
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Re: Battery charging

Post by c13dnw » Wed Feb 08, 2023 10:53 pm

This is my battery. Would you say that AGM? It states lead on it. As far as I can tell the only difference in charging AGM than normal lead is AGM goes to 14.7 volts and lead is 14.2 so doesn't do any harm anyway.
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Rusty Racer
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Re: Battery charging

Post by Rusty Racer » Sat Feb 11, 2023 9:15 am

I didn’t have an AMG on mine, so don’t always assume they have one. My Cteck was connected to a lead which was under the small removable cover in the scuttle. You can find an earth and there was a spare connection in the connector for positive.
Nice an easy to plug in and loose the charger under the bonnet. I previously connected it in the boot on a TT but never liked shutting the cable in the boot.
2018 RS4 B9 Carbon Edition
2014 RS4 B8

johnnydog
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Posts: 481
Joined: Sat Jun 11, 2011 8:24 pm

Re: Battery charging

Post by johnnydog » Sat Feb 11, 2023 2:53 pm

The Ctek MXS 7.0 charger I use on mine has a frost setting for charging in colder temperatures, which is the same setting for AGM batteries, so all in all it probably won't really matter which is used between the standard or AGM setting relative to the amount of the charge rate applied.

johnnydog
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Posts: 481
Joined: Sat Jun 11, 2011 8:24 pm

Re: Battery charging

Post by johnnydog » Wed Feb 15, 2023 3:24 pm

c13dnw wrote:
Wed Feb 08, 2023 10:53 pm
This is my battery. Would you say that AGM? It states lead on it. As far as I can tell the only difference in charging AGM than normal lead is AGM goes to 14.7 volts and lead is 14.2 so doesn't do any harm anyway.
AGM batteries are lead acid batteries - its just their construction is different. They don't leak if tipped over, delivery higher power in comparison to standard batteries and can withstand being left in a lower state of charge better, although this is not recommended for any battery. They often state the battery type on the label, such as AGM or EFB.

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