Quote:
Originally Posted by Mark963
... I never see it talked about, but using INPA has a State of Health value under the IBS menu. It's starts at something like 3.xx% and rises from there...
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I would be interested to know WHAT INPA screen you are referring to. For instance, DME > F5 > F5 > F2 PM (Power Management) Infofield 2, provides values for "Ladungszustand & Startfähigkeit" = State of charge & Starting ability, at the moment (last start), and for 1 day ago to 5 days ago (vor 1 Tag to vor 5 Tagen).
There is a LOT of data in INPA, and the problem I have is trying to correctly interpret it. As a practical matter, I have NEVER seen a battery fail to crank the starter of ANY vehicle for 2 seconds, at ANY temp > 10F, as long as its voltage measured 12.0 Volts or more. In warm weather, most will crank if > 11.9V.
Of course if it has a "Bad Cell" or internal fault, it will FLUNK the load test imposed by the Starter. It could be charged to a Voltage of 12.5 V 10 minutes after disconnecting charger. Waiting that 10 minutes is necessary for "Surface Charge" to dissipate. But as soon as you press START, all you get is "CLICK" with NO Starter engagement or rotation of engine, and your battery voltage NOW reads about 10.5 V. Charge it up again and the same thing happens.
Over the years, nearly half of the batteries I have had to replace failed EXACTLY that way. I have had a battery charger "forever" and I don't sweat losing charge in 24-48 hours due to sulfation, or age. However when the battery flunks a Starter Load test, it's DONE.
The question has been asked in another thread: "What's considered good battery Volts?" BMW basically says (E90 Voltage Supply TM) the function of the IBS and Power Management Module is to shut down consumers, wake-ups, etc. as needed. "SoC is used during key “OFF” periods to insure the battery maintains a sufficient charge to start the engine at least one more time." E90 Voltage Supply & Bus Systems (BMW Training Manual), Page 10.
So it's NOT too far from the truth that BMW considers good Battery Volts as
"ENOUGH to start the engine at least ONE MORE TIME." Since the primary purpose of the Battery is to Start the Engine (and NOT to play tunes for 2 hours after engine shutdown ;-), it may sound trite and totally BORING, but that's what auto batteries have been used for during the last Century.
The Power Management System CANNOT put MORE energy INTO the Battery during Sleep or Engine OFF. ALL it can do is prevent energy DRAIN FROM the Battery. It cannot even prevent Battery drain due to Quiescent Current or Parasitic Draw. It CAN and DOES record such Quiescent Current in the Log found at DME > F5 > F5 > F4 PM InfoField 3.
George