Refused to exchange defective product Maplin Llandudno

After yesterday purchasing rechargable batteries and charger. I unpacked the product and placed 4 of the AA batteries on charge ..9hours later still no lights to say it had been charged or any light telling me it needed charging. I took the product with yesterdays recipt back to Maplin Llandudno where I spoke to the store manager. He tested all 8 batteries 7 showed charge 1 did not . He said the 4 that were on charge were charged. I was trying to explain to him that as 3 of the others that were not on charge seemed to have power that the 4 that were on charge may have also had power before I purchased them.It stands to reason that it's quite possible as 3 of the others were fully charged which I had not put on charge! I asked for an exchange which he refused as when he tested it the light briefly came on. I explained that it was not coming on when I switched it on and it seems to be intermitant. Still he refused with a cocky attitude also adding ''well I can't sell it now can I ? ''You have opened the box'' Those were the exact words..yet this is a sealed plastic package ...just how the hell does he expect me to check the product is working without taking it out of the package!!??? Does he think I am Derren Brown ... To sum up I will not be using the store , I will be making as many aware of this terrible service as possible. I mentioned this to my partner who is manager of one of the high street store and she was shocked and agreed I was totaly within my rights to have an exchange product. Of course this is Maplin Llandudno so your rights don't seem to be of importance here!!