Well, that could be anything.
I'll be blunt and say: is the battery fine?
Also, did you put in the battery clips the right way?
Otherwise you can measure current. Put the battery only on one of the clips, and connect the other polarity to one probe of the multimeter, and the other side to the other battery clip. If you don't understand what I'm saying, then I'll make a diagram.
The battery instantly gets the blue on light and works (badly if course) with my last one. I put the battery clips in the right way, same as last time.
Everything is soldered nicely into position so i am quite unsure why.
The only difference from last time was swapping R17 and R18.