Intermittent 12V Power Loss
 

I have an issue with 12V power loss with my '07 FEH. One day I got to work and tried to lock my car via the remote and there was no response. I got back in the car and tried to start it and there was nothing. No lights, no sounds. By the end of the day I was able to start it and go home. I have seen similar threads by nothing seems to match exactly what I am seeing. Any help is greatly appreciated. Here's what I've noticed:

- I sometimes get a service brakes soon messages after starting the car. It goes away after a couple minutes, but feels like I have no power assist in the brakes. I have to push very hard to stop.
- The symptoms don't occur everytime I shut down the car, but when they do it seems to be a rough engine shutoff when I turn off the car. Also, the nav immediately turns off instead of waiting until the door opens.
- I've tried to get out of the car and check the battery voltage right away when the symptoms are occurring but I haven't been able to catch it in time.
- The battery voltage is measuring about 12.5V, I assume this means it is okay?
- I also checked the voltage with the car running, and it was about 13.5V so seems like it is being charged.

Re: Intermittent 12V Power Loss
 

Fully assess the battery. Take it to an auto parts store after letting it sit overnight and have them LOAD test it. If it's > 2 years old, just replace it.


Voltage is only the starting point to determine if a battery is healthy. Pop your hood before bed and check the voltage in the morning. 12.5V just off running is actually pretty bad.


I currently have a 12V battery that will read 12.4V after sitting for several days; however when I load test it, it drops off a cliff. if I actually test it's capacity, it has 1.6Ah of capacity when its rated for 35Ah. It clearly has a failed cell that's working just well enough to supply voltage but no actual capacity. You may find you have a similar situation.


12V battery quality has dropped off in the last several years - even the premium brands. Most are made by Johnson Controls regardless of the name on them, and they are all subject to inclusion of recycled lead, which has substantially more impurities than virgin lead. They can only purify it so much and stay economical.


Confirming the actual health of your 12V system/battery is always step one in any troubleshooting.


If the battery is good, check the connections and main cable attach points. Check the (-) cable for resistance. It should be extremely low.

Re: Intermittent 12V Power Loss
 

Back some time ago, I watched a whole series on lead acid batteries on "How it's Made". Most all lead used to manufacture batteries these days is from recycled lead and little from mined ore. It was in three parts, mining, recycling and the manufacturing of Exide brand batteries.

Re: Intermittent 12V Power Loss
 

Thanks for the help. I replaced the battery and so far so good!

Re: Intermittent 12V Power Loss
 

Glad to hear it!

Re: Intermittent 12V Power Loss
 

1 month ago, I saw a gas consumption of 30 mpg. Before that loss of power starting 1 month ago, gas consumption was normal (38 mpg).

Re: Intermittent 12V Power Loss
 

is the loss of power still present?

Have you observed recalibrations on the SoC gauge?