its due to over charging... Im supervisor of RCA tech support in Los Angeles and we have portable tvs that this happens to every now and then. Disconnect your charger from the computer when it has reached it full charge unless your using it.
Technically its still the companies fault for not warning of this potential problem. Here at RCA we will replace a battery in this condition no matter how long the customer has had the product.
Im here because the same thing happened to my macbook today. Im hesitant to call tech support after reading some of your posts though.
FYI for all rechargeable battery devices, unplug after fully charged. phone, portable tvs, computers etc.