low battery and stop light

Bought my 197 about 4-5 week ago,after driving for a while the car beeps and the low battery warning light comes on and the stop light.The guy who i bought it off told me about this,he thought it was the alternator so bought one from a s****yard and had it put on but the problem was still there.Thought the card might need going in the slot to recharge the battery as the guy told me he kept the card in his pocket(he thought it was safer).Ive been putting the card in the slot everytime but the problem is still there.Last week took the car to renault to find out what the problem was,renault rang me n said it was a wiring fault so told em to go ahead and sort it,not long after they rang back saying they had done the wiring repair but the fault was still present,then they told me they think it could be the alternator as the car had a 's**** yard alternator',after me explaining why they then said the car had an incorrect upc fitted ! I haven't a clue what there on about,renault didnt tell me how much it would cost to sort it they just said it wasnt cheap.The car is listed as it was stolen and recovered (stripped but not sure excactly what was taken off).When the warning lights do come on i can still drive the car as normal then when i get chance i just stop the engine then start it again,it used to do it about twice a day but since going to renault its doing it loads more.Just wondered if anyone had heard of this problem before ??:confused1: