Glad you figured it out, if you read some comments and replies here, you'd also find out about the stamina-battery mechanic as well as some other things.
I highly suggest browsing through our wiki to get more familiar with the game and it's mechanics.
Once you learn how a certain mechanic works, you kinda have that "oh, that's how it works, pretty logical" moment, even though at first you have absolutely no idea about it.
Have fun playing,
Cheers