I'd also look UNDER the car for a rusted out grounding strap. Google it. Obviously it is not the battery- so it is either a phantom use (interior light, windowd trying to close or per OP, maybe wipers trying to home Readmanual. Most cars have a 'battery saver" that stops all electric usage after 10 minutes. I bet there is a phantom useage or a short in one of the wires.
Try googling
Tucson + battery wont hold charge. I am 100% sure this is an ez fix. Problem is the diagnosis. Possibly the alternator is not functioning, or the voltage regulator . Nut I woould assume the mechanic wpould have tested thos things (*it's ez). Iwould start with YouTube. You are not the first person with this problem.

 

Thar is clearlly the place to start. The outside casing is obviously disconnected. It does not conduct current, of course, but it could be that in heavy rain some splashes get into trhat casing, and pool at the bottom. Causing a short. Or the ex[posed wires have rubbed themselves raw and are causing the short. . In any case, it is a cheap part and should be replaced. If it is not currently a cproblem, it will develop into one.