Minimum Battery Temperature for APU Start?

• A. -25 C
• B. -20 C
• C. -15 C
• D. -30 C

Answer: (B)

Cold-temperature performance of aircraft batteries determines whether the APU can crank reliably. The APU starter draws a large surge of current, and as the battery temperature drops, chemical reactions slow, increasing internal resistance and reducing the available current. To ensure a successful start, crews rely on a minimum battery temperature that guarantees enough cranking power. For this aircraft, the battery can deliver the necessary current at -20 C or warmer; below that, the current may be insufficient, risking a failed start. Among the options, -20 C is the threshold: -15 C is warmer and within spec, while -25 C and -30 C are below the limit and not acceptable for a normal start.