Thanks, we can at least agree on this point! :thumbup:

Funny how I asked this same question almost two years ago and you ALL were on the other side of the fence!!!! Terminators car stopped running while he was driving. The battery came loose. I told you guys that the car should have stayed running, yet everyone insisted "bmws" won't because there is too much "electrical stuff". I even offered to try this on my own X, but YOU, upallnight, got me so nervous to try it explaining that there are current spikes and what not that alternator can not correct so you would take a chance of damaging components. So which one is it? Will your BMW X5 run without a battery installed?

Always!!!!:thumbup:

NEVER remove a battery connection when the engine is running. You will not like the results of the surge damage when reconnecting it. Modules will fail, electrical components will go off the deep end. Can it be done and not have any issues? Yes, but why take the chance? THis "test" was a short cut way back in the 60's left over from post war vehicles with generators.

Loose power connections have shorted out more electrical components than anything else in history. (An assumption on my part. No actual data collected...:rofl:)

Regarding a vehicle that dies when the battery is disconnected: A good electrical system SHOULD have kept it running. But who knows what failed at the same time as the disconnect? The Regulator? The main module? The ground wire? Who knows? Maybe the alternator/wiring was DEAD/shorted before the disconnect.....

It was stated that the connection at the battery came loose. Once tighten all was well from what I remember.

I thought the car should have kept running too.

The battery dampens and filters the alternator output.

One thing that most modern vehicles do is the DME/ECU can and will kill spark and fuel if the input Voltage gets too high to protect the DME/ECU and other modules in the car in the case of a high Voltage swing. Usually 17-19 Volts it the trip point for most vehicle. No idea the exact value for BMW and I am not interesting in finding out on any of my cars.

You can arc weld with 120-200 Amps and as mentioned it is not a wise test to disconnect the battery on a modern vehicle for testing. Without the battery as a static load and filter, the alternator can do some funny things. Even filtering out AC ripple that can high peak to peak Voltages.

A $20 Voltmeter or using the Hidden OBC Menu to access the Voltage and display it on the dashboard is all that is needed. Charging and starting systems are really easy to trouble shoot as long as the EWS does not get in the way.

Learn how to use a Multimeter/Voltmeter and learn how to perform Voltage Drop testing and you can correct the majority of problems that creep up. I also use a spare pair of jumper cables to connect temporary grounds to identify and find problems.

:iagree::iagree::thumbup: