I suppose for 6 mos. you used the laptop and thus recharged it. So, how you can call the salespeople or "associate" is an idiot seems rather harsh. It worked for 6 mos. right, why is there a problem now. The shelf life of being a display unit and all included plus your 6 mos. use may gotten into the battery life down side or the charger has gotten wonky. Many times the charging port can be broken in some way also. As already offered to you, at 6 mos. I assume you have warranty, allow them to deal with it. I also assume you filled-out any warranty application during initial 1st days or so.
You can visit the laptop makers support website and check the FAQs on your issue and apply common fixes. However, don't crack open the laptop in any way as to NOT void the warranty. Understand also, batteries don't last forever and depending on prior use and yours, 12-18mos, sometimes batteries do falter for whatever reason.
tada -----Willy 