Battery drain

[INEMPLOYED]

Had the car for 4 or 5 months and the battery has never showed any weakness but after reading up on BMW the consensus seems to be that they are hard on the battery due to all the onboard electronics so I started putting a trickle charge on it after driving. I’m retired and put very little miles in the car, my usual runs are less than 5 miles but I’ve noticed the battery is at 40 or 60% capacity when I get home and put the charger on it. it’s not a parasitic draw because once it’s 100% it will hold that for days if I don’t drive.

I was thinking it’s because of the short runs but today I took my kid to school in the morning then made a 60 mile round rip freeway run, came home and picked up my son from school, I put the charger on it and it was down to 40% of capacity. The battery doesn’t show any physical signs of weakness as well as before this trickle charge regimen where I’d gone months without incident. Are these alternators some kind of smart devices where they only charge below a certain threshold or is my alternator weak or is this all normal and no need for concern? I did notice the CCA on the battery was what I though low at either 550 or 575 can’t remember

[shogun]

Moved to G30 forum. Here are some typical data for sleep mode, although your model is not mentioned, but should be similar:
Parasitic draw is often a problem. Perform Closed Current Draw Test
Maximum closed current by vehicle
E31 50mA, E32 50mA, E34 40mA, E36 30mA, E38 50mA, E39 40mA, E46 40mA, E52 50mA, E53 40mA, Z3 30mA

Performing Closed Current Draw Test
• Select proper measuring device (DISplus, MoDic or DVOM).Remember amperage draw in excess of 10A will damage DVOM.Use inductive amp probe of DISplus when amperage draw is high. When using DISplus inductive probe, clamp on negative battery cable with arrow pointing away from battery. Switch off all consumers.(It is not necessary to disconnect B- from body when using inductive probe)
• Connect (-) test lead to negative battery terminal and (+) test lead to a known good ground.
• Ensure all systems are OFF !
• Be sure DVOM is on and set in proper mode.
• Disconnect battery ground lead from body.
• Observe meter reading, wait 16 minutes for vehicle to enter sleep mode.
• Identify faulty circuit by disconnecting fuses, relays, control modules or connectors, observing meter readings. Defective circuit is found when current is below maximum closed current for vehicle being tested.

use this link for more details http://www.e38.org/battery.pdf

I am also not driving that much, I have the trickle charger always connected and a healthy battey

[INEMPLOYED]

I did a bit more searching and it appears that if it’s in eco or comfort mode then the alternator isn’t generating until the battery drops to a certain threshold, I’m gonna test sport mode and see if it makes a difference

[shogun]

Please let us know the findings of your tests.

[f355spider]

OP, what method are you using to get your battery capacity levels? Can you describe the testing method or device?
If you are down 40% battery capacity there should be significant issues with starting and operation of the car.

[INEMPLOYED]

OP, what method are you using to get your battery capacity levels? Can you describe the testing method or device?
If you are down 40% battery capacity there should be significant issues with starting and operation of the car.

when I hook it up to the charger is shows capacity, I make nothing but short runs, after only a couple stops I’ll put the charger on it and it’s 40%, sometimes 20% but there’s never any physical sign of battery problem. I also have a small digital reader that shows the same as the charger, I just got this volt tester and it seems ok


https://youtu.be/vOpoxM8E71Q

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Even after a 1 stop trip to the grocery store and back I’ll get a 60% capacity reading

[INEMPLOYED]

Found this while researching:

As I understand it, most vehicles' stock alternator / charging systems can't completely charge an AGM battery... they will only bring it to a certain state of charge. To charge it to 100% capacity, one needs to use an aftermarket battery charger that is sophisticated enough to do so.