How I fixed my SP with flickering power LED and intermittent power
Channel: makho
Date: 2019-04-06

Here's the short version: https://www.youtube.com/watch?v=G946mQCkIQc

Yes that's a GBA console but this issue is a problem with all Game Boy consoles and the solution is the same for all of them. If your power light flickers or sometimes your GB just doesn't even turn on, this what you need to do. 

Please excuse the last test, I have two identical batteries on my desk and it turns out that only one of them was charged.