Stamina Question

Hello everyone!
I'm relatively new to the game (I've been playing for 10 days or so). I have a question about stamina in the battlegrounds. What is the max stamina supposed to be? Is there a way to increase it? I looked around the forum and couldn't find an answer. I'm asking being I started with a max of 4 stamina but my friend started (and still has) a max of 2. We both downloaded the games on our ipads too and once again I have a max of 4 stamina and she has a max of 2. Are we doing something differently? Or did I just get lucky?

You may want to read this thread for more about the battlegrounds... https://forums.storm8.com/showthread....and-Its-Levels

Normally, your stamina is 2, but can go as high as 4 (maybe 5?), but you use 1 every time you fight in the battlegrounds.

I have read through that thread already and didn't quite find my answer. I know you can win more than 2 stamina by beating certain levels. So if my friend and I beat the same level and win 5 stamina, then I will have 5/4 and she will have 5/2. Does that make sense? If I leave the game alone for a few hours, I will have 4/4 stamina and she will have 2/2.