riddle - I'm the first of my kind

See me once, I'm the first of my kind
See me twice, unhealthy lives we left behind

See me once, because there's only one
See me twice, then there's something we shun

Hint:

See me once, some mistake me for a mountaintop

See me thrice, without me many devices flop

Good Luck!

_{Here are the previous riddles in this series (the solutions there have nothing to do with this one, only the process of getting there).
#1, #2, #3, #4, #5, #6, #7, #8}

Answer

I believe you are:

the letter 'a'

See me once, I'm the first of my kind

First letter in the alphabet

See me twice, unhealthy lives we left behind

AA stands for alcoholics anonymous which helps recovering addicts

See me once, because there's only one

use the word a when there is one of an item( a chair, a table , etc.)

See me twice, then there's something we shun

not sure for this part but maybe AA like a scream or shout? People tend to ignore/not help AA and in a sense shun it. Hopefully third times the charm: People in AA shun alcohol?

Hints: See me once, some mistake me for a mountaintop

A capital A looks like a cartoonish mountain

See me thrice, without me many devices flop

As pointed out by @El-Guest AAA batteries are commonly used in devices to power them