My laptop battery does not fully charge: when it is connected to AC,
it charges 30-40-50% (according to status indicator), and then the
charging led turns off and (i presume) it stops charging. Re-plugging
it sometimes increase charge
a few more percent, but not always, and usually third and consequent
are useless.  Calibrating doesn't help either... If someone can point
me to useful information on this situation this would be greatly appreciated.

P.S. If that's of any use, the laptop is Asus m3n, the battery is about 8 months
old...

Some batteries have what is called memory.

If they are not fully discharged before recharging, They take less of
a charge next time.

My electric razor did this.

The new one (had to tosss the old one) I discharde until the blades no longer spin.

Is your lap top a lithium battery?

Yes it is LiIon battery, so i presume there should be no memory effects...

A poor contact could cause this. Try cleaning with a pencil eraser. Is
the time between charges down considerably? If not, the LED indicator
may be in error. If the battery is hot to the touch after charging, it
is getting as much charge as it can handle. You may be able to get a
warenty replacement if you got the battery from a local merchant.
If you have a way to reduce the input ac voltage (to the power cube)
from 120 down to about 100 volts, the battery will take lots longer to
charge, but may charge completely.   Neil

Clean the contacts, and if that doesn't work, try putting the battery
in the deep freeze for a couple of hours before charging.  This
sometimes works, but I have now idea why