AGM battery low voltage - BMW 3-Series (E90 E92) Forum

laurentProd · 02-19-2013, 07:17 PM

Hi all !

Just a quick question :
What voltage do you read from your AGM battery, the car not running?
I have 11,7V !! Even after a full night charge using this : Ctek MXS 5.0 batt charger ...

Weird? no??

My battery is the original one, from end of 2007.

The car is cranking and starting very well everyday.
The reason I asked is that, during cold days, the engine is running a little bit rought ... I read that a dying battery could lead to that kind of problem.

(btw, I replace plugs, coils, injectors, Nox sensors, O2 sensors, and still have some cold rought starts)

Thanks !!

chromisdesigns · 02-19-2013, 07:19 PM

Your battery is due for replacement. It has nowhere to go but further down. Get it replaced before you need to have the car towed.

laurentProd · 02-20-2013, 07:10 AM

Even if the car if starting well everyday?
ouch ...

401FlaGATOR · 02-20-2013, 07:28 AM

If the battery is truly at that level then it may be bad..How are you reading the voltage? Because if you are correct, battery should be on the verge of not being able to start the car at that voltage..

If you are reading the voltage using an obd or from the car itself, try measuring the battery with a digital multimeter right at the battery terminals..Then turn on the car and take the measurement again..if you measure 11.7 with car off and with car on you have a charging voltage around 13.0 or higher you have a bad battery.

A healthy battery at 11.7 would be about 50% discharged. If you charged all night you should be at 12.0 to 12.5 in the morning if your battery is good..

This holds true whether its AGM or flooded..

It might be possible if you have a flooded battery that one of the cells may be low on electrolyte. Check the levels and add distilled water if you discover this.

laurentProd · 02-20-2013, 09:50 AM

Got AGM !

11.7v using digital multimeter.
13v or more when car is running...

I'll try to change it with a new one.

marine24 · 02-20-2013, 11:30 AM

When the car is running the alternator is providing the power, so the battery will not cause it to run rough. The battery only supplies power when starting, even if it is wearing out. The rough idle could be from needing to replace spark plugs or cleaning the intake ports, depending on mileage; especially if it's a 335.

02-19-2013, 07:17 PM	#1
laurentProd Enlisted Member Drives: E93 Join Date: Feb 2013 Location: France Posts: 42 iTrader: (0)	AGM battery low voltage Hi all ! Just a quick question : What voltage do you read from your AGM battery, the car not running? I have 11,7V !! Even after a full night charge using this : Ctek MXS 5.0 batt charger ... Weird? no?? My battery is the original one, from end of 2007. The car is cranking and starting very well everyday. The reason I asked is that, during cold days, the engine is running a little bit rought ... I read that a dying battery could lead to that kind of problem. (btw, I replace plugs, coils, injectors, Nox sensors, O2 sensors, and still have some cold rought starts) Thanks !!
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02-20-2013, 07:10 AM	#3
laurentProd Enlisted Member Drives: E93 Join Date: Feb 2013 Location: France Posts: 42 iTrader: (0)	Really? Even if the car if starting well everyday? ouch ...

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02-19-2013, 07:19 PM	#2
chromisdesigns Lieutenant Colonel Drives: 2008 BMW 335i sedan Join Date: Jan 2010 Location: San Francisco Posts: 1,742 iTrader: (0)	Your battery is due for replacement. It has nowhere to go but further down. Get it replaced before you need to have the car towed.

02-20-2013, 07:28 AM	#4
401FlaGATOR Private First Class Drives: e90 325i ZSP Monaco Blue Step Join Date: Oct 2006 Location: Pembroke Pines, FL Posts: 164 iTrader: (0)	If the battery is truly at that level then it may be bad..How are you reading the voltage? Because if you are correct, battery should be on the verge of not being able to start the car at that voltage.. If you are reading the voltage using an obd or from the car itself, try measuring the battery with a digital multimeter right at the battery terminals..Then turn on the car and take the measurement again..if you measure 11.7 with car off and with car on you have a charging voltage around 13.0 or higher you have a bad battery. A healthy battery at 11.7 would be about 50% discharged. If you charged all night you should be at 12.0 to 12.5 in the morning if your battery is good.. This holds true whether its AGM or flooded.. It might be possible if you have a flooded battery that one of the cells may be low on electrolyte. Check the levels and add distilled water if you discover this.

02-20-2013, 09:50 AM	#5
laurentProd Enlisted Member Drives: E93 Join Date: Feb 2013 Location: France Posts: 42 iTrader: (0)	Got AGM ! 11.7v using digital multimeter. 13v or more when car is running... I'll try to change it with a new one.

02-20-2013, 11:30 AM	#6
marine24 Private Drives: 07 335i Join Date: Aug 2012 Location: Southern California Posts: 74 iTrader: (0) Garage List 2007 BMW 335i Coupe [0.00]	When the car is running the alternator is providing the power, so the battery will not cause it to run rough. The battery only supplies power when starting, even if it is wearing out. The rough idle could be from needing to replace spark plugs or cleaning the intake ports, depending on mileage; especially if it's a 335.