Driving on low battery; bad for the alternator?
 

The X5's battery warning light has lit up and the welcome light doesn't turn on anymore. The car still starts fine, but if I drive in this low voltage condition, is this going to be bad for the alternator? I need to wait until next week to get it serviced. The 2008 has only 2500 miles on the odometer. It had once completely discharged before, to the point of being unable to start at all, by leaving it untouched for six months. The battery failed again, so I jumpstarted it but now it's showing a warning message and the steering wheel won't move to a position when I start the car. I'm afraid it might be hard on the alternator.

I've just read from a link in google that brushes in the alternator will burn away or wear out from working too hard, and am getting concerned...
Since this is the second time that the battery has been completely drained and the alternator working extra hard to recharge it (it seems that this time the battery is less willing to be fully charged), could the alternator be tested for any defects? How do I know if the alternator is not damaged at all?

The output of a modern alternator is electronically controlled to match demand and is protected against excessive current draw.

IF you are worried about recharging a low battery with just your alternator, Get a good battery charger and hook it up to the jumper point in the engine bay over night. Make sure the charger is designed to slowly charge the battery and cut off when the battery is topped up.

BTW whenever you don't drive your X5 for weeks (or months) you should put it on a trickle charger to keep your battery from going flat. Modern vehicles don't handle dead batteries gracefully.

Funf Dreisig

Don't believe everything you read on the internet.

Isn't it the role of the alternator to recharge the battery while the car is running? So, I would imagine that this would be okay.

The main issue with charging a nearly dead battery using just the alternator is that it isn't a very energy efficient method unless you already had a reason to drive the X5 quite a bit anyway. You still need to check the voltage to make sure it got charged enough.

Hooking up a battery charger is both more efficient and easier to monitor the battery's charge state. Most electronic battery chargers shut down automatically when the battery is fully charged and have some method to tell you this (e.g. lights, meters, etc.). The X5 has none of these nice to have assurances that the battery is charged.

Funf Dreisig

I totally agree. So, it comes down to whether a nearly-dead car battery will still be "dead" if you're only driving 15 minutes each day. However, I wouldn't think that it'll be bad for the alternator, which will continue charging the battery as long as the car is being run.

I thought the battery warning light was an indicator that the alternator is no longer charging the battery while driving. :dunno:

Just get a new battery. You won't have to worry about harming anything else or it not starting (unless there is some other reason your battery is discharging but such little use is likely the culprit).