How much is a Laptop battery supposed to last before going in red ?

Vladimir: How much is a Laptop battery supposed to last before going in red ?
I got my first laptop this days and i have noticed that my battery when not plugged in the electricity lasts for around 2 and a half hours ,also i just tested and played one game on Star Craft 2 and from 75 % it went to 56% ,is this normal for a brand new laptop .
My laptop is Acer .
So what is the supposed time of a fully charged laptop battery?

Answers and Views:

Answer by Slim Shady
That’s about average.

Answer by Paul R
The more you use it the quicker the battery will run out.If you have it turned on and just leave it the battery will last longer than if playing a game as it needs more power to run things.The more programs you run the quicker the battery will run down.Also depends on what settings you have the laptop set to,to how long it will last.Different laptops have different batteries which varies on how long they last but yours seems about average.