Final answer:
The typical procedure for APU starts using battery power allows for two attempts before a required 20-minute cooldown period for system recovery.
Step-by-step explanation:
The permissible number of Auxiliary Power Unit (APU) starts when using battery power, before needing to take a 20-minute cooldown period, is typically two starts. The APU is an important component in an aircraft that supplies power to systems and components. After two start attempts, it is recommended to wait for 20 minutes before making another attempt to avoid overheating the system and to allow the battery to recover. This procedure ensures the longevity and safety of the APU system and prevents unnecessary strain on the battery.