My doubt is that this cellphone always scanning for wifi lan compromising battery life

My wifi is not set to always scan for wifi. You can set it by going to the following:

Menu>Settings>Connections>Wireless LAN

From there set your settings. I have it so it never shows when theres a wifi connection.

I also think there is a problem with this setting.

I also have mine set up so that it doesn't continuously scan for networks, but when I go into the available networks applet, it seems to know about a list of networks suspiciously quickly.