Aux battery charging

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Tonygw

MB Enthusiast
Joined
May 30, 2019
Messages
1,140
Location
Leicestershire
Car
C250 CDI AMG Blue efficiency diesel
Hi

Just wondering, is it ok to connect a battery charger/conditioner to the aux batery to give it a charge in my 2012 C250CDi estate (S204) while in the car and connected up.

The ECO stop start never seems to work and I "guess" the aux battery isnt in good condition. I havent done any diagnostics but was just ging to try giving it a charge with a battery conditoin/charger to see if it brings it back to life.
I have a low power aldi special charger I was going to try.

But I dont want to attach it if it might cause a problem.

Thanks
 
FWIW - I connect the charger to the jump start posts (as per my owners manual) and it sorts out the Stop/Start. I don't expect that you are taking any risks if you charge the car as recommend and see what happens with the AUX.

You batteries are probably AGM so make sure of that and select the correct mode on your charger.
 
cheers will try that first then, best to do it the way the manual states
 
FWIW - I connect the charger to the jump start posts (as per my owners manual) and it sorts out the Stop/Start. I don't expect that you are taking any risks if you charge the car as recommend and see what happens with the AUX.

You batteries are probably AGM so make sure of that and select the correct mode on your charger.

That answers my question from yesterday about alternative charging points. The GT has lithium Ion batteries according to the build sheet, I might need a new charger to take care of these... but there is no one at the dealer to confirm if both or only the Aux is a lithium battery!
 
That answers my question from yesterday about alternative charging points. The GT has lithium Ion batteries according to the build sheet, I might need a new charger to take care of these... but there is no one at the dealer to confirm if both or only the Aux is a lithium battery!
Try this one.

https://www.amazon.co.uk/dp/B07PPP8H8Y/?tag=amazon0e9db-21
 
Last edited:
Main battery is lithium on my S63, to save weight!

I use a normal charger and don’t select AGM mode. This effectively constrains the charge voltage to not exceed 14.4 volts. I attach it to the jump points under the bonnet.
 
Main battery is lithium on my S63, to save weight!

I use a normal charger and don’t select AGM mode. This effectively constrains the charge voltage to not exceed 14.4 volts. I attach it to the jump points under the bonnet.
I seem to recall reading that you cannot (should not?) leave the charger connected once full charge is reached.
 
I seem to recall reading that you cannot (should not?) leave the charger connected once full charge is reached.

You should not leave it on charge at anything above the correct float voltage. A lithium battery will almost certainly have protection to prevent over charging. An AGM battery is sealed but with a safety valve. If you over charge an AGM it will gas and eventually blow the safety losing some electrolyte which can't be replaced. Every time it blows shortens the batteries life, do it often enough and the battery will die.
 
You should not leave it on charge at anything above the correct float voltage. A lithium battery will almost certainly have protection to prevent over charging. An AGM battery is sealed but with a safety valve. If you over charge an AGM it will gas and eventually blow the safety losing some electrolyte which can't be replaced. Every time it blows shortens the batteries life, do it often enough and the battery will die.

I was referring to the LI-Ion being charged on a standard charger. Ideally he should buy a charger with the correct mode.

However, good modern chargers can safely be left attached and will not overcharge. They go into maintenance mode (e.g. My Ctek). How do I know this? I emailed Ctek about the AGM mode over the weekend and got a reply this morning.
 
All makes sense now my car was stood for 4 months now stop start won’t work and battery says critical if it’s not used for a while
 
The auxiliary battery being motorcycle small charges up quickly , half an hour in AGM mode and mines charged .


Not that I've got a use for it !
 
The GT has been stood since January and it hasn't complained of a low battery yet. I'm going to wait until the dealer opens as I was recommended to go for the CTEC Lithium XS as it will charge and maintain both batteries. Only the Lithium XS charger has the function to wake the lithium battery if the electronics have put it to sleep apparently which is why its recommended.

There is a socket in my boot (which I have not seen) for the Aux battery to top that up, and then provided the main battery is maintained the aux goes to sleep to preserve itself. The GTR and Pro come with a said Lithium XS charger and the electronics are the same, I want to confirm it first though!
 

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