I had this trouble and most comments refer to tweaking the battery contact but I think that's the wrong thing to do because every time you put the atty/tank back on it punches the connector back again. This cannot be good for the battery with the constant fatigue.
the best way is to tweak the middle terminal out on the CHARGER which can be done with a fingernail. Make sure it's central because the pin can go to an angle quite easy. That way once you screw on the battery it should always be the right length or close to.