Sony WS623 has 4GB internal memory and you can further expand it up to 16GB with the help of MicroSD card.
No. Sony NS-WS623 does not have FM radio.
You can check the charging status with the lamp ( 3 ).
While the battery is charging: orange when charging is complete: green
No. Sony WS623 comes with non-removable battery.
Yes, it does have fast charging. Charge it for just 3 minutes and it will work for another 60 minutes.