When I modded my RX200 to put in the DNA200, I wanted to test it before putting it all back together, and that's what I was getting. After a little freaking out, I realised there is a brass tab that sticks out of the negative of the back left battery and the screw goes through to ground it to the board. Once I'd screwed it together, it fixed that issue.
When looking at the mod from the battery door side, try tightening the upper left screw inside the battery compartment. If that doesn't fix it, try tightening the others, specifically the two on the middle and bottom right I think. If that doesn't work, it's likely a solder connection from one of the batteries. I'd offer to take a look but I don't trust myself, so what I'd do is contact for a warranty repair or replacement, and if all else fails, contact someone who builds custom mods, unless your soldering is pretty good.
Edit: Just saw the last post, make sure the negative wire going from board to 510 isn't blocking that brass tab, I had to do a fair bit of finagling to leave enough space for the tab and screw.