Its pretty much the circle of life for a laptop to end up being constantly plugged in.
You will get the best out of any battery for about 1 year then its down hill all the way.
I'm on a 8hr Battery Net Book when New 2yrs ago.
Now i can do about 1hr 1/2
Its just how it works out.
I suspect unless you find a Banded laptop Battery your going to be throwing good money away, as UnBranded once can loose that MAX LIFE pretty quick with in months.
Normally a Branded Battery from the Manufacture would set you back the best part of £70.
One Solution ?
Invest in a Nice Extension Cable to Reach Across the Living Room to your Favorite Chair. Probably cost you about £6
Its just the Circle of Life i'm afraid.