Battery voltage?

[AlanD]

Big drive (~240 miles) two weeks ago last Saturday week (5th). Moved it on the driveway on the 8th. Not used since, dead as a door-nail this morning!

Bit annoyed, it had a new Bosch battery in it when I bought it (800A, 95Ah .. not sure if that's CLS55 spec or not). Should be able to last 2 weeks!

It read as 12.5V after I jump started it and ran it for 30 mins (12.3V about 5 mins later after playing with menu items!). Is that normal? My C55 is 12.2V from little use in the last month apart from a 10 min battery run every couple of weeks.

What's "bad" if I measure it again tomorrow?

 

[whitenemesis]

I didn't trust my CLS55 to go two weeks, even with new batteries and charge circuit checked ok. Always put it on trickle charge. Even after a longish 200 mile run the conveniences off message would come on next morning.

 

[AlanD]

Next morning!? That's soon. I've never seen any messages before and normally just leave it weekend to weekend. Nowhere really suitable to trickle charge ..

 

[whitenemesis]

Summer's warmer weather never saw a problem, come winter though ...

 

[DSB SL AMG]

You need battery tester to check if its holding a charge and good, and eliminate alternator charging issues, maybe Halfords for free check? worst case car could also have a battery drain...it should be okay for 2 weeks, maybe 3 weeks absolute max...sure i read somewhere MB do not recommend leaving a car more than 3 weeks without trickle charge.

 

[AlanD]

You need battery tester to check if its holding a charge and good, and eliminate alternator charging issues, maybe Halfords for free check? worst case car could also have a battery drain...it should be okay for 2 weeks, maybe 3 weeks absolute max...sure i read somewhere MB do not recommend leaving a car more than 3 weeks without trickle charge.

Yeah, might well bring it down if I get a chance.

2 AMGs sitting on the drive, so know well what it should last with a year old battery in the other doing fine

I wondering if they Bosch battery they put in to sell is under spec! Anyone know what a CLS55 battery should be?

 

[whitenemesis]

Handbook states 95Ah 520A AGM/VRLA type

 

[AlanD]

Handbook states 95Ah 520A AGM/VRLA type

Didn't see a spec in the user manual .. piddling it down with rain right now so I ain't going back out today!

520A vs. 800A seems rather .. different ..


What's a good voltage on the dash btw? Below what is it likely to have trouble cranking over?

 

[kid-jensen]

12.5V sounds a bit low.... Maybe the regulator is on it's way out?

I'd expect something above 13V, once the battery has recovered from cranking the engine (say 20 mins).

 

[190]

It's becoming more difficult to do a diagnostic check on modern car charging systems because many have smart alternators where the charge voltage is changed to improve economy. You will get a higher voltage on the overrun as the alternator works in a regenerative braking mode then the voltage will drop under acceleration. I've driven around with a voltmeter plugged into the cigarette lighter socket and while the charge voltage is all over the place it did rise to 14.5 volts which assured me the alternator is charging decently when it want to.

 

[andy27168]

Hi,
For info.
On my CLS55 the boot battery is no longer an AGM type, it came from the factory with an AGM but the spec has now since changed to a lead acid battery.

 

[paul73mt]

My pennies worth I have left mine for 27 days with it not moving and it started on the button. Mine isn't as flash but you may have a battery drain ??

 

[AlanD]

Yeah, worries me there might be a drain. I'll have it down in a PCS in a few weeks so can get Olly to check it out. It's either that or they've put a crappy little battery in it just to sell! Anecdotally, it doesn't appear to have a vent hole to connect the vent tube to ..

 

[whitenemesis]

The CLS55 is well known for battery issues. When I bought mine my BiL who used to manage a main dealership service centre, said if I didn't drive it daily and for significantly long journeys, it will need trickle charging. The predominant complaint from owners was flat batteries.

 

[AlanD]

Was down to 11.3V today when I got home after its 30 min run yesterday. Did a 15 min spin out to get petrol and came back with 12.5V just dropping to 12.3V as I watched. Will have cranked it twice obviously, but seems to drop rather easily!

Trickle charging isn't much of an option without a garage Doesn't it damage a battery if you let it run out completely or does it depend which type?

 

[AlanD]

Here we go, this is what's in it:

http://www.allthings.co.uk/cars_bikes/bumper/battery/WP_20161121_20_00_28_Rich.jpg

http://www.allthings.co.uk/cars_bikes/bumper/battery/WP_20161121_20_00_46_Rich.jpg

Seems to be collecting water down there too, but that's another issue!!

 

[whitenemesis]

Check the boot floor bung

 

[DSB SL AMG]

Yes, if you repeatedly drain a battery it will eventually cause damage...

Doesn't it damage a battery if you let it run out completely or does it depend which type?

 

[AMGeed]

Seems to be collecting water down there too, but that's another issue!!

Check the rubber seals that go down each side of the boot from the bottom of the rear window. Mine have started to perish and need replacing.

I have the same Bosch S4 battery fitted to my E55.
I also get the convenience function message after 3/4 days of non use in the colder weather.

 

[AlanD]

Check the rubber seals that go down each side of the boot from the bottom of the rear window. Mine have started to perish and need replacing.

I have the same Bosch S4 battery fitted to my E55.
I also get the convenience function message after 3/4 days of non use in the colder weather.

Interesting .. can this problem be solved by brute force then with a BFG 9000 equivalent battery!? (sorry, 90s geek joke) :fail

Seriously though .. bigger better?