Just came here to thanks all you guys for sharing your tips.
Was able to revive my wife's ebike battery that was left unattended for more than 2 years...
First, I tried the wheel backward just to chack that the battery led indicator was at least blinking which it did.
Did try the plug/unplug more than 60 times with no success. Green led kept showing and got bored.
This morning, did a 40 ride with the front wheel backward. Arrived at home and plug the ebike to finally see the red light on the charger!!!
I will now let it charge for a full day and hope everything will be fine.
Once again, thanks all for sharing!