Battery Dies

Hi I have an 02 sprint with a battery/alternator problem. After a couple of hours run with stops n starts the battery dies, there are no warning lights on dash n battery holds its charge once charged up. I have a battery/alternator tester n it shows no charge from alternator but it's only a simple attach to battery type n not sure I trust it. Is there a better tester I should buy or replacement part I should get? Thanks
Mark

 

Ok thanks I'll get a better meter n try testing it properly. I've looked up changing the alternator that looks a bit of a pain so fingers crossed it's rectifier or battery

 

Hi thanks for the replies n to update I've tested with a better meter. Battery shows just over 13 volts standing n drops to 12.30 when running, even lower with lights on. Rec/reg looks to have been replaced recently so tested alternator as per Haynes manual. From the three pin connector I have continuity from each wire to an earth, there was even evidence of a short in the connector so I guess it's a replacement stator. Deep joy