Battery advice.

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Matt58

Active Member
Joined
Nov 16, 2020
Messages
313
Location
Taunton
Car
2003 E55 sedan
Hello all, my main battery always seams to be around 11.8-11.9 after a few days sitting, both batteries (2003 E55) are under 2yrs old and genuine merc. CCA are down to 550 out of 850 but car still starts fine, I did have a paracetic draw from a bad alarm siren and overhead control module which completely drained the battery, this happened a while back so I removed fuses for ocm and command, plus left siren unplugged, as I use car as a daily. I’ve been checking drain on a regular basis, and drain is a constant 0.06. My question is, do I need to replace battery, and would leaving the siren unplugged cause the car any probs. I did slowly charge/condition battery, and alternator charging around 14.0, any advice gratefully received. Aux batt 12.6.
 
Hello all, my main battery always seams to be around 11.8-11.9 after a few days sitting, both batteries (2003 E55) are under 2yrs old and genuine merc. CCA are down to 550 out of 850 but car still starts fine, I did have a paracetic draw from a bad alarm siren and overhead control module which completely drained the battery, this happened a while back so I removed fuses for ocm and command, plus left siren unplugged, as I use car as a daily. I’ve been checking drain on a regular basis, and drain is a constant 0.06. My question is, do I need to replace battery, and would leaving the siren unplugged cause the car any probs. I did slowly charge/condition battery, and alternator charging around 14.0, any advice gratefully received. Aux batt 12.6.
What did you use to condition the battery and is it an AGM battery? If it’s a standard lead acid battery - and your conditioner has the feature, for example CTEK conditioners do - then it would to use the “Recond” feature. This will remove some of the sulphur which may have built up due to be depleted, and charge it up too.
 
What did you use to condition the battery and is it an AGM battery? If it’s a standard lead acid battery - and your conditioner has the feature, for example CTEK conditioners do - then it would to use the “Recond” feature. This will remove some of the sulphur which may have built up due to be depleted, and charge it up too.
Thanks for reply, it’s a AGM, and I charged it with a all singing and dancing ring charger, which also tells you what cca your battery has. Unfortunately I have no way of hooking up a ctek trickle so keep a real close eye on batt cond.
 
What did you use to condition the battery and is it an AGM battery? If it’s a standard lead acid battery - and your conditioner has the feature, for example CTEK conditioners do - then it would to use the “Recond” feature. This will remove some of the sulphur which may have built up due to be depleted, and charge it up too.
PS I would suggest doing this with both batteries.
 
Thanks for reply, it’s a AGM, and I charged it with an all singing and dancing ring charger, which also tells you what cca your battery has. Unfortunately I have no way of hooking up a ctek trickle so keep a real close eye on batt cond.
In case you do get a CTEK, please not that you cannot use the Recond mode with an AGM battery, even though the CTEK device will allow you to select both Recond and AGM. The instructions specifically tell you not to, as the desulphation process can damage the fibre inside an AGM.
 
Hello all, my main battery always seams to be around 11.8-11.9 after a few days sitting, both batteries (2003 E55) are under 2yrs old and genuine merc....
I believe that the warranty on MB-branded batteries is 2 years - check the date on the invoice and perhaps start with a warranty claim if applicable? The battery will also be properly tested by the supplier as part of the return process.
 
Car batteries don't like to be fully drained so you could well need a new one
 
I believe that the warranty on MB-branded batteries is 2 years - check the date on the invoice and perhaps start with a warranty claim if applicable? The battery will also be properly tested by the supplier as part of the return process.
Just looked at the mb invoice dec 2020, bummer.
 
Car batteries don't like to be fully drained so you could well need a new one
Yeah, I think that’s on the cards. Do you think I should get another alarm siren? Would the fact that it’s not there throw any other module? Never got any of this trouble with my old cortina.
 
In case you do get a CTEK, please not that you cannot use the Recond mode with an AGM battery, even though the CTEK device will allow you to select both Recond and AGM. The instructions specifically tell you not to, as the desulphation process can damage the fibre inside an AGM.
Would love to keep the old girl on a ctek, but have no power where the car is parked. That’s for the advice.
 
Just looked at the mb invoice dec 2020, bummer.

But does it also say how long the warranty is? It might be longer than 2 years, I don't know.
 
In case you do get a CTEK, please not that you cannot use the Recond mode with an AGM battery, even though the CTEK device will allow you to select both Recond and AGM. The instructions specifically tell you not to, as the desulphation process can damage the fibre inside an AGM.
Thanks for that. It's useful to know. I never know what to do so I keep my Ctek on "normal" charge all the time.
 
Yeah, I think that’s on the cards. Do you think I should get another alarm siren? Would the fact that it’s not there throw any other module? Never got any of this trouble with my old cortina.
You can buy a cheap load tester for testing. Mine is basically an analogue one with a heating element inside and a gauge. You flip the switch for a few seconds and see how quickly the battery drains. I think it cost less than $25

61747_W3.jpg


I don't have an answer for the alarm siren, I expect it will trip a code at some point.
 
Hello all, my main battery always seams to be around 11.8-11.9 after a few days sitting, both batteries (2003 E55) are under 2yrs old and genuine merc. CCA are down to 550 out of 850 but car still starts fine, I did have a paracetic draw from a bad alarm siren and overhead control module which completely drained the battery, this happened a while back so I removed fuses for ocm and command, plus left siren unplugged, as I use car as a daily. I’ve been checking drain on a regular basis, and drain is a constant 0.06. My question is, do I need to replace battery, and would leaving the siren unplugged cause the car any probs. I did slowly charge/condition battery, and alternator charging around 14.0, any advice gratefully received. Aux batt 12.6.

I know you have eliminated some sources of parasitic drain but 60mA still seems high to me. I don't have a figure for your car but my guess is that it's approx. double what it should be.

If those are accurate figures then 11.8 or 11.9 volts is a pretty terrible state for a battery to be in, being very nearly flat. Any length of time at that state of charge and the battery will be sulphated. You are measuring that voltage at the battery or jump start terminals and with the car as far as possible asleep. Any other way of measuring it does not give an accurate picture of the state of charge.
 
You can buy a cheap load tester for testing. Mine is basically an analogue one with a heating element inside and a gauge. You flip the switch for a few seconds and see how quickly the battery drains. I think it cost less than $25

61747_W3.jpg


I don't have an answer for the alarm siren, I expect it will trip a code at some point.
I know you have eliminated some sources of parasitic drain but 60mA still seems high to me. I don't have a figure for your car but my guess is that it's approx. double what it should be.

If those are accurate figures then 11.8 or 11.9 volts is a pretty terrible state for a battery to be in, being very nearly flat. Any length of time at that state of charge and the battery will be sulphated. You are measuring that voltage at the battery or jump start terminals and with the car as far as possible asleep. Any other way of measuring it does not give an accurate picture of the state of charge.
Yes measuring at the posts, with the car asleep for at least an hour.
 
My W211 went through a couple of batteries in as many years.
Changed the alarm siren and all's been good since.
Might yours have a redundant Tracker fitted? Just a thought.
 
My W211 went through a couple of batteries in as many years.
Changed the alarm siren and all's been good since.
Might yours have a redundant Tracker fitted? Just a thought.
Yeah that thought had crossed my mind.
 
Certain electronic modules / units go thro a shut down sequence via the canbus system on ignition switch off. if they dont then they can continue running causing a parasitic drain. they may not generate a fault code because they are otherwise functioning OK
 
also see
 

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