What is the core function of the battery light on cluster

[jsoto]

If anyone has been following my string of 12V issues.....

Anyhow, question of the day. What is the function of the battery light on the cluster

Got around to popping a new alternator in. I'm hoping this is the fix........
Never Ever got a battery light on the cluster

To sum it up.
Burned up 2 batteries
Root cause I suspect that both times, I was literally driving the car and running off the battery until it either shorted out/drained way too far/too fast. And or Alternator acts up during when the car got hot - really hot ?
Most of the daily drivers is anywhere from 16-20 miles and then back.
Both instances, when the battery died, it was a 60-70 mile trip.

When looking at alternator with MM and amp clamp, it's always been putting out power at correct V.

I've had multiple drives in between the last 2 months, but I was putting the battery on a charger whenever I saw the voltage after rest dip under 12.6. I suspect this compounded/masked my battery/capacity issues during the days/weeks I was messing with this...