Is 12.4v too low?

[bigtisas]

I measure the voltage of my car battery. It read 12 to 12.4v when the car is off and 13.4 when the car is idling. Is it too low? I heard a good battery should be around 15v.

I bought my e34 about a year ago and I don't know how old is the battery. The reason I check the voltage is because I am getting a lot of error messages contantly...engine oil low, brake lt circuit, ESD regelt. Engine oil level is fine, all brake lights work and I already replaced the brake light switch 6 months ago. I heard low voltage could cause random error mesg. Should I replace the battery? The car starts fine everytime. Thanks.

[Tiger]

Accurate test is using a battery tester... it puts a load on the battery and if it stays above a certain voltage under load, it is good. This is a free test done at Autozone... Pepboys or PartsAmerica... they do this because they want you to buy new battery from them.

[Qube]

Rough guide... Open circuit voltage State-of-Charge in %. Estimation of a 12V flooded lead acid car battery.

Test the battery at room temperature. Allow 4-8 hour of rest after charge or discharge (eg. running)

12.65V 100%
12.45V 75%
12.24V 50%
12.06V 25%
11.89V or less Discharged

Or more info (including simple load calc with terminal voltage)... http://wiki.xtronics.com/index.php/Sealed_Lead_Acid_Battery_Applications

[Claude]

I measure the voltage of my car battery. It read 12 to 12.4v when the car is off and 13.4 when the car is idling. Is it too low? I heard a good battery should be around 15v.

I bought my e34 about a year ago and I don't know how old is the battery. The reason I check the voltage is because I am getting a lot of error messages contantly...engine oil low, brake lt circuit, ESD regelt. Engine oil level is fine, all brake lights work and I already replaced the brake light switch 6 months ago. I heard low voltage could cause random error mesg. Should I replace the battery? The car starts fine everytime. Thanks.

I would gest your batterie is not that bad, i've got almost same reading on mine tested the same way (in summer time). You're also right low batterie voltage could give you that kind of symptoms but you should also suspect the state of your "Check Control Module" http://www.bimmer.info/forum/showthread.php?t=35348&highlight=check+control+module this could be the source of those wrong error messages.

Before checking / opening your CCM you may previously fully recharge your batterie and see if that make a difference.

[bigtisas]

I took the CCM out and checked the solder joints. They looked ok. Put it back. For some reason, I have not seen the brake lt circuit, ESD regelt message in the last a few days. :-) I hope that's it. Thanks for the info guys.

[shogun]

if all that does not help. change the capacitors
http://bmwe32.masscom.net/johan/dash_caps/dash_caps.html

[uscharalph]

These cars are hard on batteries.

[PaulJ]

The original battery in my '91 535i lasted 10 years. The replacement had been trouble free since installation when I sold the car last year. I can't say my car was "hard on batteries". I was certainly disappointed with the engine cooling system (blown head gasket) but I never had any issues with the electrical system. My $.02.

Paul

[shogun]

Apparently there is a difference where the battery is located, engine room, under seat or in trunk room (in general now for BMW). I have the main battery under the rear seat and additinally a smaller one (EOM) in the trunk.
Looks to me that those not located in engine room last longer. 7 years I had the first one in, more than average.