R230 SL500 Battery issue.... I know, don't roll your eyes!!

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pioneercollector

MB Enthusiast
Joined
Jan 23, 2022
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1,998
Location
Bath
Car
SL 500
OK, I am aware of the consumer battery going flat and offline if you do not regularly use the car, and i have never had an issue with the car starting ...ever. Last week the car was completely dead, couldn't turn the key, hazard lights not working etc, so i jumped started the car ( using the starter battery under the bonnet ) and she fired up after around 10 minutes of having charge fed in... Took her for an hours drive, everything was working perfectly.

Parked up and one week later the car was completely dead again....

The consumer battery was replaced 2 years ago by Mercedes. My question? is this a sign that the cranking / starter battery is dead? or could there be something more ominous happening?

Strange that i have never had the completely 'flat' issue before ....

I am going to jump start her again and get her over to my Independent MB mate, but first thought that i would check in with the experts here first ;)
 
Sounds like you might have a parasitic drain. The usual culprit for this is the alarm module.
I would still fully charge the main battery and either have it tested, or test it yourself if you have the equipment.
It sounds like you are charging ok, but it wouldn’t hurt to get that tested at the same time.
Hope it gets sorted quickly (and inexpensively). You wait all winter for this time of year!👍🏻👍🏻👍🏻
 
Thanks Ted,

Yep all year ..... sigh

I did think about the alarm, but to be honest ( shhhhh ) when i put the car away i never lock it ... just in case situations like this arise and i cannot get in ( My lock up is not an aircraft hanger, it is quite snug with a gert big car in it! )

Charging and testing is the best way forward, Just found it odd that this issue has just happened .... oh well roll on the dry stuff ....
 
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I've spent hours trying to trace a comsumer battery drain on mine. After a week its down to 6 volts.
So I've now fitted an electronic battery isolator unit. It's remote control so you just press a button after you lock the car and the consumer battery is disconnected. It comsumes 4 millamps so will take weeks to drain the battery.
Also if you forget to set it. It automatically operates when the battery voltage drops to 11.8 volts.
I've had it a month now and so far so good.
 
Hi There - That sounds like a really good idea! Where did you get that from? And does it cause any issues with the car computers having the battery off?
 
Thanks Ted,

Yep all year ..... sigh

I did think about the alarm, but to be honest ( shhhhh ) when i put the car away i never lock it ... just in case situations like this arise and i cannot get in ( My lock up is not an aircraft hanger, it is quite snug with a gert big car in it! )

Charging and testing is the best way forward, Just found it odd that this issue has just happened .... oh well roll on the dry stuff ....
If the battery is completely flat, the alternator won’t charge it. You’ll need to put it on a charger to get some volts into it that the alternator can sense.
 
OK - That makes sense, I have a feeling that the issue may be a relay in the boot that directs the power around - Just something that someone mentioned to me and his description of the issue did sound identical to mine.... hopefully it is just a knackered battery !!
I may dig out the errant battery and stick it on charge for a while.

Thank you all for your tips and ideas - most helpful
 
Hi Pioneercollector
Sorry only just seen this reply. I got it from eBay £30 Type in electronic battery isolator its a small blue box. The only down side is I suspect the alarm is no longer set? Not that I'm bothered about that......
 

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