Help on this witchcraft :)

Hello everybody!

I was wondering if someone can help me with a problem that I’m dealing here.

Unfortunately some battery were forgotten (for long) inside of a Lavalier mic sender (Sennheiser sk100 g2) and the time allowed the acid to work/damage on some parts and I decided to clean as much as possible and even to replace a micro-switch (tough work).

Well... everything looked cool except for the fact that the device, after "cooling down", wouldn’t turn on again, showing only the bat sign and a random trace on the display, kind of crazy stuff and not a official warning.

After some "phisical reasearch" - blowing it with the air dryer to evaporate quicker the fat cleaner to take out he flux, it was working fine, after cooling down, same story again.

At the end I got to the conclusion that the part  that is broken/malfunction is this part on the imagem with the code SMI040M4. When I heat it up (leting the welder almost touching it) the device works 100%. When it cools down, again the malfunction.

(by the way, when I touch it with conductivity to the ground - with a metal part or finger -  it reboots the equipment, is it normal?)

Im a beginner in this world and I don’t even know what is this piece exactly? Another problem is that after googling it I didn’t find the latest clue about it . 

Any clues of what the hell Am I dealing here? Where can I get this piece and... is it easy to replace? Looking at the spot (and how I think is welded) I predict already a nightmare

All the the best and thank you for you help.