What was found
APU BATTERY CHARGER SHORTED INTERNALLY AND CAUGHT FIRE WHILE AIRCRAFT POWER WAS ON. POWER WAS REMOVED AND FIRE WAS PUT OUT. FIRE WAS NOT SEVERE AND NO DAMAGE WAS NOTED TO THE AREA. BATTERY CHARGER WAS CONTAMINATED WITH SKYDROL FROM ECOLOGY BOTTLE THAT WAS NOT INSTALLED CORRECTLY. BOTTLE WAS INSTALLED CORRECTLY AND BATTERY CHARGER WAS REPLACED IAW MM. OPERATIONAL CHECK WAS GOOD AND AIRCRAFT WAS RETURNED TO SERVICE. (SW21200501060)