Screeching noise when turning on?

Hi :slight_smile:

I want to buy a “defect” OP-1 for a fraction of the retail price, but I need some guidance to contemplate my ability to repair this unit. From what I have gathered from the seller, It has been sitting in the attic for ≈2 years, and it wont turn on properly. He has not connected it to mains (from what I can tell) and it makes a loud screeching sound through the speakers when turning on. No lights no nothing.
He mentioned “opening” the unit, but i have no idea if he actually opened it while it was turned on (for repairs???) or if he meant “turning on” (Won´t judge his English).

If it really is the battery, it´s an easy fix, but if the DSP board is fried it´s a catastrophe…
I know this is far fetched, but could anybody give an analysis based on these very very small details? (Detectives welcome!)

Any suggestions on further things to ask him or ways to fix it would be very welcome!