You could have a defective battery, there are lot's of low quality ones on the market. Certainly install the new one when you get it.
It could also be the charging circuit. However, before we go there, I would inspect the ferrite bead (FL7500, the one on the bottom left is the red square). It is inline with the charge state going back to the charge circuit. It may have been damaged when you played around the connector area. If you have a multimeter, measure it to see if it is a dead short (it should be).
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Then get back to us with your findings.