How to remove a stuck screw on battery socket?

Tried with penetration oil. But the screw isn't directly fixed on the frame so I suspect that the oil didn't really sink into the thread.

I don't know when did this happen. Mayb it's the vibration locked it in place. I think the screw is semi-stripped as well because of my trying. I still get enough leverage but it doesn't even budge a bit.

I once tried to upgrade my bike with a half-opened battery socket. In the end, the wiring cost me 4 hours because I couldn't fully reach the cables. So I decide to get the screw out before I do anything stupid this time.