WiFi is a huge drain on the battery. Even though you might not be connected to a WiFi network, the WLAN sniffer on Nokia keeps searching for wireless networks in the background (i.e. if you see a WiFi available indicator at the top). I would suggest you turn off Wireless LAN discovery by going to Settings —-> Connection —-> Wireless LAN —-> Turn off “Show availability” and turn it on only when you need to connect to the internet.