iPhone 2G battery drains fast under 20% level
I bought an used iPhone 2G. I believe the battery is OK because i went through a full charge and it lasted about 6 hours of use (and 2 days standby) which I guess is normal. Nevertheless, I dont think the iPhone is reporting the battery levels correctly. For instance, it stays at 100% for a long time, close to an hour of use. Then when it hits the 20% level and displays a warning it drains all the way down to zero very quickly. In 10 to 15 mins of use the battery goes from 20% to 0%. Is this a known issue? Can this be a symptom of a deffective battery?
Thanks in advance for any advice and/or shared knowledge about this..