IT'S IN THE LAST LINE

I usually come in twos threes or fours 
Usually available in all kinds of stores 
Spend a lot for me and I will last a long time
Who am I you're wondering in this rhyme 

I make all your electronics come to life
A remote control for example or electric knife
All different sizes usually with the letter A
When I am spent I'm tossed and thrown away

If it wasn't for me your camera wouldn't operate
To the wall clock in your kitchen I'm his best mate
So what am I and what can I possibly be 
I am dear friend a most humble battery