Su-kam Inverter — About inverter battery

My name is Yogesh Garg.I live in Kalanwali, Distt. Sirsa, Haryana.Last year i bought a new Su-kam inverter battery from a local Su-kam Dealer.But after 7-8 months that particular battery started causing problems, as the battery back-up remained only for 5 mins.So we approached to that particular dealer for change of the battery.I think we call that person for atleast 2 months&after 50-60 calls, he replaced our Su-kam battery with a local one&told us that Su-kam comp. manager is not listning to him.So thats why he is facing the problem.So almost after continously complaint for 4 months now my battery has been changed, but now this dealer is demanding 500 rs.even though he changed our battery within guarrantee.So i am wondering why i have to pay him.Even though whole procedure harras us a lot.i am totally lost confidence in Su-kam comp.I hope company will take this very seriously&solve our problem&plz tell me also why i have to pay 500 rs.