Powers off after flashing twice

Hi,

I found many threads on the wide internet about controllers sometimes flash exactly twice and then turning off.

Some say it is about the battery not being recognized of being perfectly fine and yes, the batteries ARE fine, double, triple and quadruple checked, since in every other thread i found, people still think it is the batteries fault.

I also used another battery holder-thing from another working controller. Then i come across about the metal thingy you on this battery holder thing which you can bent so it connects better. tried that too, no dice.

So I opened it up today, cleaned it with alcohol, resoldered some connection which kinda looked fishy. but still, it keeps blinking twice and shutting off.

On reddit I found a suggestion about plugging in a play and charge cable without any batteries, letting that sit for a day. tried that too, no luck.

There is also no way of returning it since I got the controller from a friend.

I really want to repair this thing.

Any help out there? :/