Everyone has heard about the battery sudden drop cases. Conclusion of reports in different forums is: Batteries started below 100% can sudden drop to 0% if a) they have not been fully charged b) they have been charged some time ago c) they were used twice and removed from the aircraft between I want to have a more close look at c) because its not obvious why this happens in that case. a)+b) its just possible they had already low or even lower voltage then % shown. But HOW does a battery flewn from 100% 4,3v--> 60% 3,8v which is removed then and just a few hours later used again loose the voltage in the meantime so that it shows 60% but may have only 3,5v left so it shortly falls to 0% then. The voltage is always shown correctly. Is this normal for a healthy battery or does this case already show a faulty battery itself? As I had this case with always the same battery which also started to get major deviations and voltage warnings my conclusion would be that this sudden drop will not happen generally with all batteries but be the first indication of a faulty battery.