One top contact button on my i2 is slight receded (seems firm though). It won’t contact some batteries properly.
How do I open it without breaking it? Anyone done that?
Those plastic snap together items are a pain when you don’t have a clue how the latch hooks work or where they are.
Nitecore i2 charger ? Use fine slotted screw driver to dig out the 4 round foam studs, 4 screws to open it.
From there you can take out the main board holding by a single screw, take a look inside what went wrong 
Tried the foam buttons but was not aggressive enough.
A couple ridges on the plastic housing support the + contact button. The affected side was either a bad cast, mangled in assembly, or possibly a tad melted, maybe from getting too warm with a NiMh charge. I didn’t like the way it charged NiMh, they got too warm. Not a problem with lithium.
A bit of tape support and it’s fine again.
Agree with the NiMH charging part, while at it after opening the charger, for both of my i2 & i4, I clipped off all those plastic ridges on both inside of the ventilating area, give more warm air out now.
Glad you solve it, cheers !