Every time I recharge my sony vaio, it'll recharge up to 100%.
However, in the morning as I unplug it from the recharger, the battery life is always at 80-89% when I begin to play. Why isn't it at full battery?
How old is the laptop battery? If it has been used many times or is an older battery, it may be working perfectly fine. Batteries wear out over time and use and will slowly lose some of it's capacity over time. The link above explains in detail about battery condition and life.
That article however is very technical, so let me find you a more lay man terms explanation.
This is a quote from a battery reseller that explains it well: (http://www.bixnet.com/batterytips.html)
They are selling a product, so of course they are going to say you need a new one right away. So what can you do about it? One way is to use a piece of software that can tell you more detailed information about your battery and help you perform battery calibration. This is a free product:
You can also accomplish this for free by basically charging the laptop all the way and then letting it discharge all the way. Then charge it all the way back up. In other words, a full discharge cycle. It will not restore lots of battery life, but it will help make sure the battery it running at its best.
EDIT: You stated that the laptop was about a year old. That sounds perfectly normal then if it is a year old. I have had the same thing happen to many new laptops after a year of use. If you are experiencing battery life times that are too low for your needs, then it would be time to get a new battery. Otherwise, the battery sounds like it is working as expected. It will slowly lose life over use and time.
The are some laptops that don´t charge their batteries until they fall down to a specific level. For example, MacBook Air starts to charge the battery when it´s under 95%.