A question about car batteries…

[A930Rocket]

The traction control and brake indicators on my instrument cluster have turned on, on my 05 BMW 330. Using INPA, I have a few codes that I’m working on, one of which is electrical (overcharging?).

I checked my 51R battery with the engine off and I got 13.17v and with it running at idle, I get 14.00.

How is it my battery is registering 13.17v? Shouldn’t it be 12.6 with no load and the engine off?

Edit: how is it my ABS – DSC system voltage is seeing higher than 18v If I’m seeing 14v at the battery at idle?

Codes below:
5DF7 ABS-DSC: System voltage > 18 volts dsc_mk60 Stability system MK60

5D97 ABS-DSC: DSC sensor, voltage supply dsc_mk60 Stability system MK60

5E43 ABS-DSC: Steering angle sensor, internal dsc_mk60 Stability system MK60

5E24 ABS-DSC: Pressure sensor dsc_mk60 Stability system MK60

[WPOZZZ]

Do you have a dedicated battery tester or are you using a multimeter? I just changed the H7 in my 997 this weekend because the car just sits and I didn't leave the maintainer on it. My tester was getting weird reading, so I said F it and got a new battery. Everything good now!

[A930Rocket]

I’m using a multimeter.

[masraum]

You can put a "surface charge" on a battery. If you charge a battery at 13.8V for a bit, it'll show near 13.8V immediately after taking it off of the charger. I don't know how long it takes for that to normalize, if it's a matter of minutes or hours or what.

When you load test a battery, that'll kill a surface charge pretty quick. If you have a load tester that simulates starting a car, one or two tests will normalize the battery (assuming no charging is happening).

I wish cars still came with real Voltmeters, Oil Press, and Temp (water or oil) gauges. I'd pay $300 to swap out my gauge cluster for one that replaces the useless analog speedo with oil press, oil temp, and volts gauges

[pwd72s]

Steve nailed it. Dittoes on the gauges...

[A930Rocket]

I had it on my battery maintainer, so maybe that’s it?

I’ll leave it off and test it again tomorrow.

I installed a dedicated water temp, oil temp and oil pressure gauge on this car.

[masraum]

Originally Posted by A930Rocket

I had it on my battery maintainer, so maybe that’s it?

I’ll leave it off and test it again tomorrow.

I installed a dedicated water temp, oil temp and oil pressure gauge on this car.

Sweet! I've installed gauges in lots of cars over the years, even basic, pedestrian cars. My Boxster's got a water temp gauge, a tach, and 2 speedos (digital and analog). It would be fairly easy to install a voltmeter if I could find a good place to put the gauge. There's nothing to a Voltmeter. Installing oil pressure is much more of a pain. My car has an idiot light, so I'd have to install a T to keep the idiot light and have the pressure gauge. I believe some folks have installed a pressure gauge in the wart on the dash after taking out the stopwatch which makes a ton of sense. I honestly don't trust that the water temp gauge is undamped. I think that a lot of gauges these days are heavily damped. When miatas first came out they had a real, honest temp and oil pressure gauges. Then mazda made them non-linear and heavily damped. So the temp gauge, for instance would read cold - middle/good - too hot. I suspect lots of companies have done that because it saves them lots of time and money. I really miss the gauges out of my old '88. They were all accurate. I could tell the temp, oil pressure, oil level, etc... all at a glance.

[SCadaddle]

Same faults (DSC and Brake light on) in a recently acquired 2001 330CI. If you'll search the symptoms on youtube, you'll find a video of a fellow discussing the very issue and apparently (especially on the convertibles) there is a wiring connector near the front of the drivers seat that can corrode/bad connection and cause the issue. I haven't dug into it yet.