Each portable device is equipped with the battery, without it the mobility advantage cannot be reached. The most common type is a Li-ion battery with durability limited to approx. 500 charging cycles which means 2-3 years depending on the usage. Cells inside the battery are getting older and the capacity gets naturally lower. The first sign of cells decrease is shortened performance time until the moment when the only way to work on your laptop is to keep it connected to the charger for the whole time. As a result its the biggest advantage has been lost. One of the most effective solutions is to replace the faulty item with the new one.