Mazda Repair: the battery warning light comes on, nissan maxima, warning light

Question
please help me joshua.. i know you work on mazda but i'm sure you have the knowledge & expertise to help me out

I drive a 92 nissan maxima with 209500 km
3 months ago with 208500km, my mechanic installed a new alternator but the battery warning light still comes on. He then tells me i have to replace the warning light system .. i think this guy just taking me for a ride. It already cost me a total of $450 to replaced the alternator and a hole in the tailpipe. Now he tells me i have to cough up another $100-$200 to fix this battery warning light.. (i didn't do it) and one more thing he screwed up installing the alternator at first.. my car got all smoked up because one of the belt got caught on the alternator and the belt snapped.. he later fix it and gave me a new belt

The car is working fine for 3 months but the warning light still comes on.. the car stalled at 209500km while i was waiting at a green light.. i had to tow the car to another mechanic // he replaced the distributor cap and now the car is running again but still with the battery warning light on.

I already tried disconnecting the battery cable for 15 minutes .. once i drive again the battery warning light pops back on again.

when i put the car gear at park (P) the battery light doesn't come on.

when i step on the brake the battery light sometimes go on and sometimes it doesn't.

when i put the gear at park(P) and step on the accelerator to rev the car
500 rpm > no battery warning light
1000 rpm > no battery warning light
1500 rpm > the battery warning light goes on again

when i shift the gear from park(P) to drive(D) with my foot on the brake pedal.. the battery light will come on in a dim way not very bright.

once i start driving around the battery light will come on and off .. and sometimes stay on


please help me out ..
please give me some idea of what's causing it

thank you

Answer
the battery light comes on warning you that the charging system isn't working if you've recently had the alternator replaced make sure it's not faulty and have the battery checked, if both those or ok then i'd say your warning light i acting up on you you can just simply take the bulb out if you want