Sony Vaio PCG-FX501 Instruction & Operation Manual page 22

Using your notebook
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The battery pack supplied with your computer is a lithium ion battery and can be recharged any time. Charging a partially discharged battery does not affect battery
life.
The battery indicator light is on while you use the battery pack as a power source. When the battery life is nearly depleted, the battery indicator starts flashing.
For some software applications and some peripheral devices, your computer may not enter Hibernate mode when battery life is low. To avoid loss of data when
using battery power, you should save your data frequently and manually activate a power management mode, such as Standby or Hibernate.
When the computer is directly connected to AC power and has a battery pack inserted in the battery bay, it uses power from the AC outlet.