Charging issues

Hi All my Rangie had been in my garage for sometime. When I went to start it the battery was flat so connected it up to another car to jump. It started but as soon as I disconnected the jump leads it died. The battery was about six years old and was planning on changing it with a new battery it started first time but after a short period the battery was drained so I had the alternator overhauled and fitted back in the car. The issue is still here appears to be some kind of intermittent charging problem. Has anyone else experienced this or any idea what it could be.