Hi. I am newbie user. My second hand n900 i bought a week ago has power issues Battery is nokia BL-5J. I measure battery with the app Advanced Power 0.5.0-3. I charge with a usb cable. (the n900 came withno charger :-( Having battery full after a 5 minute call droped to 75% (wifi and gps off) I noticed big drop and 2-3 times after a call. So : is my battery uselless? And if i'll need some tips what to watch for if i buy a replacement . Alexandros.