Dead battery

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Matt58

Active Member
Joined
Nov 16, 2020
Messages
309
Location
Taunton
Car
2003 E55 sedan
Evening all, I was playing with my new E55 this morning and thought I would try and use the feature for testing battery before startup and alternator health once started, unfortunately battery reading 11.6v and car turned over but failed to start. I've taken main battery out (mercedes/varta) out and charged up to 12.6v I will leave over night without charging, it does seem to be losing charge already (down to 12v in 1hr) so I'm assuming it's the main battery. My question to all is I've got a yuasa 100ah 900a wet battery that's in my Audi RS6 C5 ( selling after chrimbo to pay for new ride) which is only 3 yrs old, can I use that battery short term to check if the battery is the cause and until I can get the correct battery from mercedes. The only other cause I can think of is that the boot catch was stuck up, so maybe car thought boot was open (sedan) and the lights have stayed on and drained battery. From what I can see the battery manufacturer date is 2014 from what I can see, but I'm not 100% on that. Luckily I have the day off tomorrow but need to sort ASAP, so would really appreciate anybody's help, thanks.
 
I think that's a good idea, not sure what your original battery specs are but that sounds plenty big enough.
Have you tried Tanya Batteries for a replacement, they have been used by several members for quality batteries ?
Car Batteries - Motorcycle Batteries - Leisure Batteries - Cheap Prices!
Also have you invested in a smart charger, they are relatively cheap and can help to maintain and restore battery health.
 
I think that's a good idea, not sure what your original battery specs are but that sounds plenty big enough.
Have you tried Tanya Batteries for a replacement, they have been used by several members for quality batteries ?
Car Batteries - Motorcycle Batteries - Leisure Batteries - Cheap Prices!
Also have you invested in a smart charger, they are relatively cheap and can help to maintain and restore battery health.
Thanks very much for the advise, original specs on AGM battery are 92AH 850A just being cautious as I don't know a huge amount on the electrical side of these cars and don't want to make things worse. Do you know if I have to register a different or new battery to the cars systems? Thanks again.
 
Your battery is shot. Just had this on my CLS55. Got a new Yuasa AGM battery from my local motor factor for £155. All good now.
Yuasa is a great brand.
 
If you use the same spec battery as the Merc one you don't need to code it.
Mine struggled to start a few weeks ago but charged it up a couple of times with my smart charger and now its back to normal.
The battery is a Varta and also a 2014 version.
You will pay dear if you buy from your dealer, check out Tanya price first, mine is around £150.
battery.jpg
 
If you use the same spec battery as the Merc one you don't need to code it.
Mine struggled to start a few weeks ago but charged it up a couple of times with my smart charger and now its back to normal.
The battery is a Varta and also a 2014 version.
You will pay dear if you buy from your dealer, check out Tanya price first, mine is around £150.
View attachment 106016
I put my reg into the Tanya website, but nothing available for my car?
 
Your battery is shot. Just had this on my CLS55. Got a new Yuasa AGM battery from my local motor factor for £155. All good now.
Yuasa is a great brand.
Thanks, what is the spec on your yuasa battery? Same as original? Cheers Matt.
 
I put my reg into the Tanya website, but nothing available for my car?
For some idea of your needs try euro car parts , that tanya site isn't the best based on reg numbers. I'd not use a wet battery long term , some mercs have a higher output alternator and your wet battery won't be wet for long.
 
What is the part number on your battery ?
 
Thanks, what is the spec on your yuasa battery? Same as original? Cheers Matt.
If you go to the Yuasa UK website you'll find the spec. Then just find the local Yuasa dealer and away you go. I think my Yuasa has more CCA than the original.
 
Evening all, I was playing with my new E55 this morning and thought I would try and use the feature for testing battery before startup and alternator health once started, unfortunately battery reading 11.6v and car turned over but failed to start. I've taken main battery out (mercedes/varta) out and charged up to 12.6v I will leave over night without charging, it does seem to be losing charge already (down to 12v in 1hr) so I'm assuming it's the main battery. My question to all is I've got a yuasa 100ah 900a wet battery that's in my Audi RS6 C5 ( selling after chrimbo to pay for new ride) which is only 3 yrs old, can I use that battery short term to check if the battery is the cause and until I can get the correct battery from mercedes. The only other cause I can think of is that the boot catch was stuck up, so maybe car thought boot was open (sedan) and the lights have stayed on and drained battery. From what I can see the battery manufacturer date is 2014 from what I can see, but I'm not 100% on that. Luckily I have the day off tomorrow but need to sort ASAP, so would really appreciate anybody's help, thanks.
Hi Matt
You didn't mention how long you charged the battery for or what current it was taking but if it was down to 11.6volts it probably needs at least an all day or all night charge. Battery capacity is normally quoted at a 10 hour rate so an 80Ah battery nominally needs 10 hours at 8 Amps from flat to be fully charged though the charging rate falls as the battery charges so in fact it will take longer than that.
If you measured 12.6v while it was on charge or just after, that doesn't tell you much about the batter, it would be the voltage of the charger and battery circuit which is higher.
It might be worth leaving it on charge for 8-12 hours or until your charger switches to float mode before you condemn it.
 
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Hi Matt
You didn't mention how long you charged the battery for or what current it was taking but if it was down to 11.6volts it probably needs at least an all day or all night charge. Battery capacity is normally quoted at a 10 hour rate so an 80Ah battery nominally needs 10 hours at 8 Amps from flat to be fully charged though the charging rate falls as the battery charges so in fact it will take longer than that.
If you measured 12.6v while it was on charge or just after, that doesn't tell you much about the batter, it would be the voltage of the charger and battery circuit which is higher.
It might be worth leaving it on charge for 8-12 hours or until your charger switches to float mode before you condemn it.
Thanks very much for explaining things, I've used a ultimate speed ulg 3.8 b1 battery charger, which I've just read if for a acid battery, hope that's compatible with a AGM battery, if not I've prob made things worse, if not I'll charge overnight, I don't know if you read my previous post on swapping battery from my other car to see if battery is the culprit?
 
You didn't mention how long you charged the battery for or what current it was taking but if it was down to 11.6volts it probably needs at least an all day or all night charge. Battery capacity is normally quoted at a 10 hour rate so an 80Ah battery nominally needs 10 hours at 8 Amps from flat to be fully charged though the charging rate falls as the battery charges so in fact it will take longer than that.
If you measured 12.6v while it was on charge or just after, that doesn't tell you much about the batter, it would be the voltage of the charger and battery circuit which is higher.
It might be worth leaving it on charge for 8-12 hours or until your charger switches to float mode before you condemn it.

The above is very good advice.

It takes a long time to fully charge a big battery and it's no use measuring the voltage just after taking it off charge. You need to let it rest for several hours or overnight to dissipate the surface charge which would otherwise give an unrealistically high voltage. Either that or turn the headlights of for a few minutes, let it rest for few minutes and then measure the voltage.

I don't see any problem at all in swapping batteries and it wouldn't matter if the battery wasn't the exact same rating.
 
Thanks very much for explaining things, I've used a ultimate speed ulg 3.8 b1 battery charger, which I've just read if for a acid battery, hope that's compatible with a AGM battery, if not I've prob made things worse, if not I'll charge overnight, I don't know if you read my previous post on swapping battery from my other car to see if battery is the culprit?
I'm sure the only difference between an AGM charger and lead acid is marketing, your charger is fine but leave it on all night as it has a low output at 3.8amps.
 
I'm sure the only difference between an AGM charger and lead acid is marketing, your charger is fine but leave it on all night as it has a low output at 3.8amps.
Oh that's good news, thought I'd made things worse.
 
For some idea of your needs try euro car parts , that tanya site isn't the best based on reg numbers. I'd not use a wet battery long term , some mercs have a higher output alternator and your wet battery won't be wet for long.
Cheers, thanks for advice.
 
If you go to the Yuasa UK website you'll find the spec. Then just find the local Yuasa dealer and away you go. I think my Yuasa has more CCA than the original.
I'll have a look, thanks for info.
 
Hi,
Just a bit of info.
I have a MY 2006 CLS 55, the official EPC states originally had a AGM Main Battery, now it states it should have a lead acid, why this changed I am not sure especially as the small aux battery at the front of the car is still an AGM (I have read that the BCM - Battery Control Module received or should of received a software update might explain it).
As I have had the car for approx. five years now I originally replaced the lead acid that was in it when I bought it and despite MB Dealer telling me it should be a lead acid I replaced it with an AGM, as an attempt to solve a small battery discharge it seemed to have (I have a CTEK Bluetooth Battery Monitor).
Replacing with an AGM I feel was the worse thing I did as the discharge rate increased (according to the CTEK Bluetooth) despite the mA drain from the battery not increasing.
The AGM seem to lose initial capacity very quickly, but then this loss slowed down, I never let it drop below 40% so complete picture was never really understood, it only lasted about 2-3 years and I have now replaced it with a lead acid and the improvement was immediately evident and the battery maintains the % charge a lot better even after 2 -3 weeks without a low battery warning which the AGM could never do.
Additionally my understanding is a normal charger will never be able to charge an AGM battery to its full capacity, I believe this is due to the higher voltage and AGM type battery is charged at.
My advice listen to MB if they state AGM then fit an AGM, If Lead Acid then a Lead Acid, and if required make sure you're charger will specifically charge an AGM
 
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