I had the same problem. I would push the button and nothing would pop up. What I ended up doing was pushing the button, while wedging a pin in between the silver part and the colored back of the phone.

Lay the juke face down on a solid surface. then push the battery latch button and pull up at the same time. you may need to hold the sides the your free hand but do not block the top. the battery pack should just pop up. to replace the battery pack just make sure the gold contacts touch and push down all the way until the battery latch button pops though the hole

Just get rid of the Juke its non-stop problems:(