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      05-15-2009, 07:50 PM   #50
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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Originally Posted by 808MGuy View Post
I assume you mean you received it from Braille with a reading of 12.3V. Did you try charging it? Does it ever come back to 12.8V (fully charged)? How long does it hold that voltage before it's down again? A few days? Weeks?
I am not sure what my battery voltage was from the factory. I can tell you that according to support folks there the output it has now ~12.3 is not normal nor within spec. I did not charge the battery. The only charging it gets in my case is from the car itself. The alternator output runs at about ~14.X volts, which should be perfect for charging any 12V nominal battery. Mine simply never gets to 12.7-12.8. It is 12.3 after hours of driving and at more or less the same level after being parked over night.

Originally Posted by 808MGuy View Post
Someone mentioned above that the low battery indicator comes on after 3 days. That tells me that either something is wrong with the charging system, which is unlikely because its not a isolated incident, or the battery is being taxed so much that its being discharged to the point where it can't make a full recovery. Once that happens, your only solution is to replace the battery. It seems that our cars have a pretty large electrical load so to try and support that from a 31A/h battery seems to be asking a lot.
Do you disagree with my contention that the only thing that should be lost with this battery is the ability to really push it and push it when cold? Leaving the car parked for a couple days is inconsequential compared to lights+stereo+cold weather starting.

Let's do some math. Lets say HP was right about 50 mA to keep CA and other idle processing going. Heck, let's double that just to be conservative. 100 mA x 72 hours (3 days) ~ 7 Ah. What does 7 Ah mean to a 30 Ah battery. Well at such a low current draw over a longer period of time (the 31 Ah spec is at 20 hours) the battery will have even a greater Ah rating probably 25% higher meaning effectively ~39 Ah. 7 surely isn't anywhere close to 39. As I see it the issue here is voltage as delivered, voltage stability (possible QA issues as lucid pointed out) and perhaps the voltage standard from the factory.