[HPR]

The car is a 2015 X3 F25 35i. After changing the oil and resetting the oil change reminder the vehicle won't start. It ran fine yesterday and was driven over 200 miles at interstate speeds this past week.

* To no avail, I tried the system reset of disconnecting the battery
for an hour
* NAPA 90ah AGM battery is 18 months old
* Vehicle is on a battery tender when not in use for a week or more
* Dash warning indicators say adaptive headlight malfunction and deep
battery discharge
* Headlights flash and I can hear relays click when I try and start
* Headlights are bright and accessories work
* A review of BimmerLink codes indicate problems with the air bags,
footwell module, and DSC. Errors change as I clear the
codes and try to restart
* I have not tried to jump start it

Any ideas before I have it towed for troubleshooting and repair?

[pungo]

What is the battery voltage

[HPR]

Originally Posted by pungo

What is the battery voltage

voltage reads 11.75.

With the symptoms I'm starting to think the BST may have failed. No accidents, huge potholes, or anything else that may have caused the BST to activate. I'm not sure how to check the BST for failure. My X3 has the power distribution module sitting on top of the battery and the BST portion of the power cable appears to be in tact.

[HPR]

[QUOTE=HPR;30130004]I'm not sure how to check the BST for failure. My X3 has the power distribution module sitting on top of the battery and the BST portion of the power cable appears to be in tact.

I guess I could take a multi-meter and check for power across all of the + terminals on the power distribution block?

[pungo]

The BST disconnects the battery from all the wiring so if the BST went, you'd have zero voltage to the car
BTW, 11.75 ~30% state of charge so really low, charge it up to see if you can raise the voltage, if not it's time for a new batt.

[Bdavi011]

Try starting it with a jump start. Seems to me like the battery is done for, it's weird for all those codes to pop out randomly.

[HPR]

Originally Posted by pungo

The BST disconnects the battery from all the wiring so if the BST went, you'd have zero voltage to the car
BTW, 11.75 ~30% state of charge so really low, charge it up to see if you can raise the voltage, if not it's time for a new batt.

My understanding is the BST disconnects the battery from the starter and alternator but allows accessory circuits to function. It's been on a battery tender overnight so I'll see what that does. Also, the car doesn't even try to turn over. Headlights flash and relays click. Battery is only 18 months old, but it's not unheard of for them to go bad that soon. Maybe I'll try and jump it to see what happens.

[richardodn]

A battery tender may not have the capability to charge that battery up. Also, it's likely an AGM battery and it's recommended to use chargers that support AGM. I recently bought a CTEK MXS 5.0. This is essentially the manufacturer branded version of the BMW maintainer charger. An alternative might be one of the NOCO Genius chargers. The Genius5 and Genius10 models on Amazon look plenty capable.

[HPR]

Originally Posted by richardodn

A battery tender may not have the capability to charge that battery up. Also, it's likely an AGM battery and it's recommended to use chargers that support AGM. I recently bought a CTEK MXS 5.0. This is essentially the manufacturer branded version of the BMW maintainer charger. An alternative might be one of the NOCO Genius chargers. The Genius5 and Genius10 models on Amazon look plenty capable.

Thanks for the heads up. I checked mine and it's a Battery Tender brand which says its compatible with AGM batteries.

Got the car started and monitored battery voltage for about 20 minutes of alternate idling and engine revving. Initial voltage reading was a puny 12.4 volts. The battery slowly discharged down below 12 volts. Leads me to believe I've got an alternator/voltage regulator problem. It's into the shop in the next few days for a professional evaluation.