Ford Cargo Hand brake and brake problem?

Hi everyone. I have a problem with the air brake system on the truck. If /-when I start (empty tanks) it takes a long time to fill. The right side fills much quicker than the left. Then after I have released the handbrake I can use the breaks only 2-3 times then there is not enough air and the handbrake activates. This happens while driving. I then have to stop and wait untill all air is drained while the handbrake is on and after a while start and wait again for the air to fill. It is as if a switch is activated when using the brakes and the air keeps on escaping. Only a fresh start (to stop and wait untill all air is released) makes it return to it original possition. Also on the battery side a reservoir is located. What should it be filled with. I thought brakefluid but on the other side a much bigger reservoir is located and is nicely filled with brakefluid.

all help is appreciated.