iPhone still drawing amps with no battery attached?

Hello everybody;

I have in my possession an iPhone 6 which was damaged when it fell into the sink. The LCI was tripped and turned red. Upon removal of the logic board and inspection of all the components under a microscope, there appears to be no issue. No burnt out components, no corrosion. So first I toss everything separately (display, casing, motherboard) into a bucket full of silica gel beads for about 5 hours to remove all the water/moisture out of the parts. I then tried using a new display, new lightning connector, as well as a new battery, and every combination of those two with the original battery, connector, and display. However, no response whatsoever from the device.

The only real lead I have so far is when I use a USB tester, the amperage is at 500 mA. When I remove the battery and test it again, the amperage stays around 300 mA (give or take 20 mA) for quite some time without change. I suspect that the issue may be hidden underneath an EMI shield and I was unable to find it with an initial inspection. So my next step is to remove the EMI shields and have another look at it along with having it cleaned in an ultrasonic cleaner.

Before I proceed though, I was hoping to get some advice on where to possibly look. Anybody have this issue before and can give any pointers in the right direction as to where I should begin looking?

Any help would be greatly appreciated! Thank you!