No problems with my two (ordered camera and extra battery as soon as preorders opened, so they're about as old as possible for an LP-E4N. But they're just LiPo batteries and they do go bad, have cells die, etc. Almost certainly the battery, not the charger.
If it's having to re calibrate regularly then that suggests that one or more of the cells is failing. The calibration function is there to balance up the cells to each-other.
I think the writing is on the wall for that pack, sorry.
Yes, one of my two batteries went bad. Nobody knows why, even Canon.
I was shocked to learn they do not even have warranty.
I suggest sending it to Canon and seeing what they say, just do not expect miracles.
Added:
My problem was different in that the battery would just shut down unexpectedly. And you cannot force a calibration on the charger. Hopefully this is something they have changed.