lg rd6300 low battery,shutdown
 

i've one lg rd 6300 which works fine while charger is connected,but as soon as I remove the charger display shows "low battery shutdown".battery is fully charged & shows 4.2v.Yet handset does not get properly on.I've also changed battery as well as charger,but no result.Help me please-the set is not water damaged or dropped. very much confused & puzzled.it's very urrrrrrrrrrgent.