One for the elec.techs Forester

The battery charges when the engine is running. Check the battery with a multimeter, when the car is off you would read about 12 volts. When the car is running you should read about 14 volts.

If you meant moonroof (as opposed to moonlight) it should work fine when the car is running unless your battery and/or alternator are a little dodgy (check by using a multimeter as mentioned above)

Note often the sunroofs (or moon roofs) have intermediate stages.

My legacy the sunroof will open fully with one press (and hold) of the button, but when you go to close it the roof stops halfway until you release the button then repress it. This is normal.

Hope this helps

Mike

They are both wrong, but the first fellow is almost right, while the second one should never be allowed to give anyone advice ever again.

Your battery gets charged whenever the engine is turning. More RPMs means more charge, but it still charges at idle.

Load has no effect unless it changes the RPMs. All the generator cares about is how fast it is spinning.

Having the light on makes it charge a tiny bit slower, but the effect is too small to worry about.

Your battery gets discharged when it supplies electricity with the engine off. The domelight discharges it slowly, the headlights faster, and cranking the engine fastest of all.

If you want to see whether I know what I am talking about, see my webpage at

Pretty close but.... at idle it's marginal. There are stories of people caught in traffic jams having their car die from running the air conditioning and hi power stereo while sitting for long periods. The battery runs down and the car dies even though there is no indicator light.

I agree with nothermark: running the heater/air conditioning blower, the lights, and one or two other things can draw more current than the alternator can supply at idle.

I recall that many years ago--and by that I mean 60+ years ago--before all cars had voltage regulators it was common belief that on a long trip it was wise to run with the lights on in order not to overcharge the battery. Whether that was ever necessary or just an old wives' tale, I dunno. But some of these beliefs die hard and advisor #2 may have been delivering advice that is no longer good if it ever was any good. I suspect it was already obsolete by the 1940s.

i am *not* an electrical engineer, but the charging system, even on today's cars, is very simple.

the alternator is driven by the engine, and produces electricity; the faster it spins, the more electricity it produces. as far as i know, most alternators are designed to work best at more than 2,000 rpm, so normal driving (not idling or stop-and-go) will charge your battery, and staying in a lower gear will also increase charging (easy to do on a manual transmission).

unlike older cars, most models today have lots of "features" that will drain a battery, even while the car is parked. you should either make a habit of driving your car more often, or consider using a trickle charger to maintain the battery while it's parked.

i'm not sure what the one person meant by "cruising", but the key to charging is engine rpm, so that doesn't sound right. and to the best of my knowledge, there's no control involved other than a simple solid-state voltage regulator, so any "load" would only waste some of the electricity, thereby reducing the power available to recharge the battery. likewise, "free-wheeling" would also just decrease the alternator's output.

i wouldn't just "suspect" low voltage - a voltmeter is a cheap (under $20) and useful piece of gear. get one and use it!

Had an alternator that showed proper voltage and amperage when running, but would slowly discharge the battery in city driving, turned out 3 of the 4 diodes in it were burned out, but the one good one was enough to fool even the alternator testing machine. Have the amperage/voltage output checked at idle speed. Ed B