Hi Boris,
hifiengine.com has the factory service manual for your radio, you just need to sign up to be able to download it:
https://www.hifiengine.com/manual_li...llit-650.shtml
The radio has a built in charger based on the LM317 voltage stabilizer chip. It can be jumpered for 9.05V or for 9.35V output, depending what type of rechargeable battery you have in the radio.
There is a Si diode in series with the battery when it is charged, so the charging voltage on the battery would be less by about 0.6V from the jumpered voltage.
It is all in the schematics.
Regards, Peter