Hi, I drive a 2003 Q45 and it appears that the charging system is not working. I can start the car with a jump but the battery does not charge with driving.

Assuming that the battery itself is OK and can hold a charge (which I have yet to prove), what simple steps can I take to find the problem before I take it to a shop? I'm a bit mechanically able but don't have the diagnostic tools or know how to do a thorough charging system test.

Could it just be a fuse? The problem started soon after I partially dismantled the center console and central dash to get the CD changer out. Maybe I blew a fuse in the process.

Any recommendations appreciated.

You want us to guess??? Only way to determine problem is to TEST components like battery/alternator/key off power consumption.....without doing that any answer you get here is just a guess.........my first GUESS would be that it is a aged failing battery.

If you have a volt meter, a quick check is to check the battery voltage with the car off, and then at idle. Off should be about 12V, idle should be around 14.4V.

Heath

Q451990, thanks for your helpful reply.

I do have a voltmeter somewhere.

If the voltage does not rise when the engine is running, does this indicate that the battery is not being charged?

Yes.

This isn't the end-all, be-all test - but it's a good start. If you see no rise, you know the alternator is not charging. If you see a voltage rise, then you need to think in terms of load testing the alternator to make sure it's holding up under a load. If your battery shows 12.xx VDC with everything turned off, and then drops way down during starting, then you can be sure your battery is shot - assuming it was properly charged in the first place.

Good luck!

Heath

The 2 decimal places after the 12.xx are extremely important as those with a temperature chart show the EXACT charge condition of the battery [unloaded].
http://www.buchanan1.net/lead_acid.shtml

12.00 volts at 77F is only 50% charged whereas 12.63 is 100%