my EX3 came with a standard BPU30 with wich I always had problems (would discharge very quickly if left on the camera of course with power off) but now the engaging system is gone, the release button is depressed and doesn't want to come back up, so the battery is "loose" although it does make contact OK if you have it standing in a tripod. Has anyone had this kind of problems, is it possible/easy to release the "release battery button" without having to send the camera back to Sony??!
It sounds like the battery release return spring is either stuck or broken. I had a look at mine and it doesn't look to be a particularly robust mechanism. It also looks like one would have to take the back of the camera apart to get at it. Since I'm not a camera mechanic I doubt that I would want to try. Even if you did attempt it you'd be left with camera parts all over the table and you'd still have to phone Sony and get them to mail you the broken battery release piece(s) you might find. You could try pushing on the battery release block found on the upper right corner of the battery back wall and seeing if the release is just stuck. I'm assuming you can remove the battery because the release is depressed anyway.
With the battery of my EX3 removed there are 4 small screws on the back wall of the battery box but I suspect that if you loosened those whatever is attached on the other side of the wall would fall off. Then you'd really be in the soup. If your EX3 is still under warranty then send it back to Sony. If it isn't, then find an authorized Sony repair facility in your area.
It's easy for me to say "send to Sony" because my Sony zone office and repair facility is only 15 minutes away. It may not be so easy for you.
I had the same problem a while back and had to jiggle the battery up and down slightly to get the spring to engage and securely hold the battery in. That annoyingly lasted for about a month, then it just went back to operating as it should.
I did one even better, when sculpting the pluck foam inside of our Storm cases, I left some tacky surfaces after spray-gluing the layers together. Naturally some of that adhesive over time found its way onto a couple of battery packs, one of which got lodged in the camera. I got it out, but it has successfully gummed up the battery release works too. Thankfully I was able to get it cleaned up.
The return spring inside this battery release mechanism does seem a little weak. Once I got everything all cleaned up and wiped clean, it freed up okay and has worked to this day.
pushing on the battery release block found on the upper right corner of the battery back wall, releases the button. For now it will have to be, every time I take out the battery, will have to do that otherwise the battery will not engage.