Battery Grief

[Clarksonvalley]

The car gods must be angry. I replaced my 10.5 year old BMW battery with a new BMW battery (this thing weighs a ton). Everything was fine again until the next day - now nothing electrical works. Does the BMW security system not like its power shut off and, thinking thieves are at work, disable the power from the battery? I have not driven the car since replacing the battery as I am reworking the leather on the drivers seat and the seat is out of the car. Need help here.

[Clarksonvalley]

I did not think that a new battery could be bad, but I just checked it - 1.026 volts between positive and negative terminals. Could there be something in the car draining a fresh battery in one day? I have all interior lights switched 'off' at the respective switches and all doors are closed anyway. And yes, the headlight switch is off - key is not in the ignition. Any ideas?

[whiskychaser]

Interior lights left on? Car 'not going to sleep'? Trickle charge the battery and hope you can bring it back to life. If you can, connect up and start looking for the circuit which is dragging it down.

PS you will know it isn't going to sleep if your window switches are still illuminated 20 minutes after you remove the key.

[Clarksonvalley]

I've got the battery tender on it now. I have the center console and the driver's seat out for the Leatherique work, so maybe I did something taking some switches out. When I get it charged, I'll put an amp meter on it and start taking fuses out - there is a drain going somewhere.

[Clarksonvalley]

I have 11.19 volts on the battery now - after recharging with the 'Battery Tender', the current flow is 0.19 amps. Interior lights are not on. Is 0.19 amps enough to cause the battery to drain overnight?

[whiskychaser]

I have 11.19 volts on the battery now - after recharging with the 'Battery Tender', the current flow is 0.19 amps. Interior lights are not on. Is 0.19 amps enough to cause the battery to drain overnight?
11.19v is only 40% charged. So if you have, say, a 70aH battery, it should in theory take 147 hours to go totally flat. I'd still want to know where the drain is though

[Clarksonvalley]

OK - I used my 'clamp-on' amp meter on the positive red lead from the battery and got a 0.45 amp current flow. Removing the fuses one by one from the under hood fuse box did not make any difference in the amp reading.

[Clarksonvalley]

The battery is a 90 AH unit.

[Clarksonvalley]

How do you figure a 11.19 volt battery is 40% charged and how did you arrive at the 147 hours to drain it?

[whiskychaser]

How do you figure a 11.19 volt battery is 40% charged and how did you arrive at the 147 hours to drain it?
You can check what voltage you have against a battery charge table to get the percentage. A fully charged battery is 12.6 volts. Which is handy because the acid in it has an SG of 1.26. I only mention this as I prefer to us a hydrometer if possible. Unless you let the battery stand for a few hours before you took that reading, you will probably have less than 11.19v.

If you have a 90 aH battery that will give 90 amps for an hour. If its only 40% charged you only have 36 amp hours. 36/0.45 = 80 hours. And then it is completely dead. It may not be a linear as that but it gives you a good idea. IIRC, Bentleys says you are OK with a 500mA discharge but I have to say that my old E34 didn't have any. Neither does my E46. Actually, we have two of them and neither of them do.

[Clarksonvalley]

Great - thanks for the information. Having taken all of the fuses out one by one and still having an amp draw of 0.45, can you suggest any place else I can look for the dark current?

[shogun]

you have to wait about 16 minutes with doors closed so that the general module is in sleep mode. Then start measuring.

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 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

[Clarksonvalley]

Shogun,

Thank you - just what I needed. Let me get back to you.

[genphreak]

It'll be alright. There are ciruits that can stay on, worn water valves I think are the most common cause of persistent draw: if your drivers' temp dial is set to max cold and the valve has failed it will be stuck and can draw current all night long trying to close. There are other things, check any 3rd party wiring too...

[Clarksonvalley]

Evidently, the battery I bought from my local BMW dealer was really low on charge. It took (3) days on my 'Battery Tender' to get it fully charged. Works great now - we are on a 4,000 mile cross country trip as I write this, so the test is if my 1995 540i with 229,000 miles will faithfully make it.

[632 Regal]

Evidently, the battery I bought from my local BMW dealer was really low on charge. It took (3) days on my 'Battery Tender' to get it fully charged. Works great now - we are on a 4,000 mile cross country trip as I write this, so the test is if my 1995 540i with 229,000 miles will faithfully make it.


If it's black I will trade you on return. 209K but a 530.