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Old 03-03-2013, 04:49 PM
magnumforc magnumforc is offline
Officially Welcomed to the 'Fest
Location: Carlsbad, CA
Join Date: Feb 2011
Posts: 199
Mein Auto: 2011 535i GT
Originally Posted by jadnashuanh View Post
It can take up to about 3-hours for a battery to 'settle' after a charge and prior to that, could see something up to the mid 13-volt range, depending on the charger, so anything you read before that point is misleading. An AGM battery is fully charged when it reads in the range of 12.72-12.90vdc after settling. This also depends on the temperature...the lower the temperature, the lower the voltage. That indicated is for 'nominal' room temperature of 68-degrees (the international standard for 'room' temperature). Now, put the vehicle under some load, and that voltage could drop a little (or maybe a lot if the load is high). What would be more interesting would be to monitor the current leaving the battery with an ammeter.

Keep in mind, a high quality DMM might have an accuracy of <1%, but it's not unusual to have it be 2-3x or more (5% on a cheap one is not unheard of) as the price comes down and the time since calibration (if it ever was done well or at all) has occurred.

Then, consider that unless you take the floor up in the trunk, you're measuring in the engine compartment which is probably at least 12' of cable, and a couple of connectors from the actual battery, which can drop the voltage as much as a couple of tenth's of a volt when everything's perfect.
I appreciate your expertise for sure. What I am finding is that it is apparent that BMW either did not charge the "new" battery when they installed it or the vehicle is sucking juice out of the battery like crazy faster than it can be fed by the "inefficient dynamics" scheme that BMW has initated. If BMW had replaced the battery as stated, and it was up to required voltage, it seems incomprehensible that the voltage could drop precipitously to the point where electronics would fail due to low voltage during a less than 15 minute drive home from the dealer in 70 degree weather. And, then find that by charging the battery for 8 hours at 1.25 amps, the electrical faults magically disappear. And that BMW can't find the source of the problem with their multi-thousands of dollars of wonderful electronic diagnostics and "trained" technicians.

Thus, we shopped for a Range Rover this weekend. Not that that will be the end all of all vehicle problems, but I haven't heard they have these electrical issues. After two of these 535 Gt's, we're about tired of the story about the electrical systems not being able to keep up with the needs of tha car and the requirements for a charger to be tethered to the vehicle. The recent explanation that the battery wears down incrementally and with all the wonderful electronics in the car, it will never tell you it's going to have a even after 400 miles of driving, and the battery allegedly charging, you can have the same issue. Brilliant engineering? Not in my book.

I wonder how people feel when others see they have to keep their 75K vehicle on charge so it will start in 70 degree weather? Foolish? Idiotic? No, I just tell my neighbors it's a BMW and fewer of them will even consider buying one. They see the light...or maybe the dimming as it were.

Cheers and be safe out there.
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