Battery not charging at any base

Ok...so..
The battery isn't charging when at the homebase.
So...I took it to a base that I know works as I have 3 roombas with each their own charging station.
Still not charging but the roomba that goes to this base does charge.
Cleaned off the contacts - failed
Reset the roomba - done but still won't charge.
Took the battery out of the failed roomba and installed it in another one of my other roombas - battery charges. I put the battery back in the original roomba - fails - no charging.
For the hell of it I ordered another battery - failed - still won't charge.
Placed new battery in other roomba - works- battery charges.
I know it's making contact with the base because when the defective roomba moves to the charger it stops BUT the light stays green ( doesn't flash orange to indicate charging is active) The battery indicator slow flashes but then it disappears along with the green lit power button telling me no charging is happening.
I checked the contact pins and they are secure. No movement.

So...What say you guys?