[Resolved]  Huawei 2900 — battery

I bought huawei 2900 mobile for using my tata connection on march 26,2009, & after a few month's as now the battery is just ready to blast as it's going oversized, & amazing fact is that the phone was not in use from past five-six month's the battery was stored apart from the instrument in it's original box. ...
when we took the phone battery to service center .Aditi electronic's nit, faridabad. they are not accepting the battery under warranty..they are giving a reason that the battery may be left near fire or may be in sunlite heat for a few day's thatwhy it's coming oversize..now as it was stored apart from the instrument now it cannot be used in phone....
IT"S A PRODUCT PROBLEM HOW BATTERY BECOME OVERSIZE WHILE NOT IN USE..?