In order to see if a laptop battery is in need of replacement versus just in need of conditioning, you have to make the battery go completely dead.

When in Windows, by default when it thinks the battery is low it automatically goes to standby, thus preventing the battery from going all the way down to completely dead.

The problem is: if you don't run it on the battery often enough, meaning that you typically have it plugged in during use, it builds a history of seeing the battery go between say 100% and 98%. It eventually decides through its adaptive circuitry that the battery must be going dead if it drains to anything less than 98%. So you have to show it that in fact it is not dead until it goes to 0% by actually running it down.

So to run it down, you cannot be in Windows. The way to do that is turn it on (unplugged), repeatedly press the F8 key until it goes to the pre-boot screen that gives you trouble-shooting options, use the up arrow key to change the option (which stops the countdown), then let it sit until goes off when the battery is dead -- no matter how much it beeps at you.

Then plug in the charger for a good long charge. Repeat the process and you should see increasing capacity.

If doing this procedure makes no difference, then the battery is actually worn out and needs replacement.