1993 Jeep Cherokee problems starting and battey discharging

I have been having a problem for the last couple of weeks. Started when I returned to my car and it wouldnt start - was turning over but wouldnt start - day befroe I was travelling. So I left it in the a garage for repairs and a service and it has come back with a number of problems the worst being that the battery keeps going dead.
At first I thought it was something I left on, so I had it recharged and was very careful to make sure nothing was left on. But teh problems continued about every 2 days. When the car drivers the volts stay around 14 and it has no problems but left over night it can die. I was recharging the battery and it stopped recharging anymore, so I bought a new one thinking that it might have been the battery after all but after one day the new one has died also. I have just recharged that one and try again and it showed power (air con worked etc) but when I tried to start it didnt turn over, and now there is no power at all.