I just got one, and the vendor gave me the BILL unlike most apple products this one does not seem to have a SERIAL NUMBER PRINTED on the connector! it only says model a1433 emc 2590 which upon quick google search is there on every such product.. DO I need to keep that bill for availing the warranty? If i loose it I loose the warranty? well, first apple product I bought that does not have the serial number on it. Help guys!