Is there a power ON /OFF switch on the HyperJuice battery?

HyperJuice (Version 1)

There is no power ON/OFF switch on the HyperJuice battery.  
To turn it on, just simply plug the MagSafe Charging Cable into DC Out port and the other end go to MacBook.  
To turn if off, just unplug the MagSafe Charging Cable from battery.

HyperJuice 1.5 and 2

You will need to press and hold the power button for about 4 seconds to turn it on so that it can start charging your MacBook and USB devices.

To recharge the HyperJuice battery, just insert the charging cable. You are not required to turn it on first.

No action is required to turn the battery off. The battery will turn off automatically if it is idle (not charging or discharging) for a while.