Exide Batteries — dealer is asking for 500 rs service charge during the warranty period

sir,
i purchased inverter and battery on 14th jan 2008 fm motor agencies corporation at gree park new delhi.after some time i faced problem with my battery regarding back-up.
he then collected the batterry from my place and now he is charging 500 rs as service charge, although my warranty period is not expired.
pls help me out as soon as possible.