Renault Scenic central locking working intermitantly

renault scenic 11 the central locking works with key card occassionally but is more likely to operate successfully when sat inside car but will then pack in completely and not work at all but never when you need to lock or unlock car in normal useage have change batteries in cards but still have above faults any ideas would be most welcome .forgot to mention i,m getting thecard battery low message on dash but as previosley stated batteries are new thanks.