Starter battery empty again after 8 hours of charging?

Moin, my car was moved very little mostly only with short distances. Yesterday it can not start because the battery is empty. When voltage measurement shows the multimeter 9.6V I then took out the battery and connected it in the apartment to a charger (a very cheap one from Absaar). Although the battery is detected and charged, after c.a 1 hour shows however the charger that the battery is defective and the charging process has been stopped Have read in the network that a battery This seems to help, charging takes much longer this time, the charging current increases continuously(14,4V) and battery capacity also (according to the charger 80% charged). However, after 10 hours of charging time, the charger shows again that the battery is defective. The battery has only 10.7V again. What can this be? Can I still save the battery? Maybe with a higher value, the battery can be used to save the battery. to the charger of CTEK try greetings