1992 Other Volvo Models Trouble Starting the car

Some times when I try starting my volvo 480ES 1.7 the renault engine my starter motor will not turn just a clicking noise. When it does that the only way I can start it is to bump start it. Other times it will start fine. There is a meeter on the battery which shows discharged. I have no battery warning light and all the fuses seem fine. Your reply will be most appreciated. Thank you