car battery light

[FredFranko]

Hi,

I had my battery, alternator and belts changed recently but when i now start the car with the headlights on, radio on, heating on and put the car in reverse or drive gear (automatic gears), the battery light indicator turns faintly on. The battery light is stronger when i have more of these on ie headlights, radio etc. Am i just overloading the battery (is this faint light common) or do i need a strong battery or alternator for the car. The car hasn't had any trouble starting.

Thank you!

[MagicRat]

This is somewhat common and normally not a big concern unless your car has never done this before.

Alternators do not produce full electrical power when the engine is idling, in the 600-800 rpm range. The engine must be turning at something like 1500 rpm to produce full power.

In your case, the electrical devices you are turning on are consuming more electricity than the alternator can supply at idle, and are sucking the extra power out of the battery. This is what the dashboard light is telling you.

When you put the transmission in gear, the rpm's drop even further, making the battery's loss even greater, and the warning light gets brighter. Of course, when you drive, the engine spins faster and the alternator now can produce more than enough power for the accessories. The extra power will flow to the battery and charge it up until its full.

Car batteries are fine with supplying a bit of etra power for short periods of time with no harm. This situation is not a concern for you unless you intend to be idling the car for long periods of time with all the accessories on If you do that, eventually you will depleat the battery and the car may not start until you drive the car and charge the battery up.

Many auto manufacturers have made alternators that look identical from the outside, but have different rated electrical outputs. If you car never showed this warning light before then its possible the mechanic has replaced your car's alternator with one that has a lower rated output, or the alternator is defective.

It is also possible the alternator belt is loose or slipping.

I would suggest you return to the mechanic and report this problem. Have the belt inspected. If it's okay, demand the alternator be replaced with one that has sufficient capacity so the warning light will not come on.

[FredFranko]

I will definitely take it to the mechanic just to be sure the belt is not loose or slipping. I don't recall this happening to the car earlier.
Many thanks!!