Why is the battery being discharged even when the VAIO computer is not turned on?

Why is the battery being discharged even when the VAIO computer is not turned on?
The computer has been fully charged. A few days later, the computer is turned on again and the battery has been half discharged.

There will be battery consumption even if the computer is not being switched on. The lithium ion battery pack will still be used for the following purposes when the computer is being switched off:

1. The operation of the circuit of a microprocessor and data transfer.
The battery pack of VAIO is also a device equipped with a microprocessor that monitors the state (the amount of battery remaining, recharging/charging current values, temperature inside the pack) of the battery pack and has the function to transmit that information to the main unit every given time.

The power is consumed, as explained above, even when the battery is kept detached from the machine as well as when it is attached to the machine.
Spontaneous discharge, which drains the power of battery, also occurs depending in whichever environment the battery is being placed in. Therefore, battery consumption during power off is a normal symptom to some extent.