Then it's not the battery.
It's not cranking because the starter is faulty (most likely). If it were the battery, the lights would dim because the battery would be giving up its last drops of juice to the starter. If the starter is not cranking because of the battery being too drained, everything would dim dramatically.
Look at the indicator eye of your bettery. It's right on top. It should be green.<img src="http://members.roadfly.org/sagan/sigjq.JPG">
actually it may be the battery I just replaced the
original in our 2001 530i because it was reluctantly holding a charge. By the way all the interior and dash lights came on, it just didn't have the juice to turn the starter.
With a new Interstate in there it is starting fine.
I recommend a BMW battery tender for the days away from running the car...
Rapid clicking or one click?
All along I was thinking ct001 was saying he just heard one click. Upon rereading, you are right, he says he heard “ a clicking”. The “a” told me one; the “ing” tells me more. I’ll assume he meant the classic rapid clicking.
With rapid clicking your description is very good. Rapid clicking is most often a weak battery, and it’s the solenoid sliding and bottoming out due to the electromagnetic force it generates. As you describe, when the voltage from a weak battery drops too low (because it’s momentarily being sucked up by the starter), the spring in the solenoid pulls the plunger back (overcomes the weak electromagnetic pull). That cycles and creates the clicking. That's my vision of the process.
In that case will the lights dim? My guess would be that they’d flicker pretty noticeably. I’ve experienced this several times in different cars over the years (never in my Z4) and I recall lights diming noticeably.
But, all along I was thinking that ct001 only heard a single click. If that were due to a battery being too low, the battery would have to be much weaker than in the rapid clicking scenario. In the one click scenario (assuming the click is the relay), my understanding is that the battery is so weak, that when the key is turned, power goes to the solenoid, but there isn’t even enough power to engage it. Therefore, whatever power there is, gets sucked up by the electromagnetic windings of the solenoid.
So in the one click scenario, I’d expect not only the lights to dim or go out, but I’d expect the radio presets to be lost and the clock to be reset to 1:00 as if the battery were disconnected. Over the decades, I’ve experienced both the rapid clicking (low battery) and the one click (mostly dead battery).
Re: Rapid clicking or one click?
" I’d expect not only the lights to dim or go out, but I’d expect the radio presets to be lost and the clock to be reset to 1:00 as if the battery were disconnected."
If the voltage gets low enough for the clock to reset and the radio presets to be lost, you can be virtually assured that the starter solenoid will disengage (due to the low voltage) and you will get the rapid clicking.
Re: Rapid clicking or one click?
Read through the posts and still could not decide if it was the battery so I wanted to post my experience.
BMW Z4 2.5i started slow and finally would make a clicking noise. Checked the battery indicator and it was green. Lights worked fine, all indications were the battery was good but still would not crank. It would just make a clicking noise.
Tried to jump the battery but did not turn over. Only when I turned the headlights off from automatic to off did the Z4 actually crank and start. Thinking this is strange I tried it again and yes it seems the headlights eat up too many amps to start the vehicle from a jump. Not sure why just giving the facts.
Took the battery down for a deep core charge but was shot. Replaced the battery and everything seems to be working fine.