Almost crash today

[zhurui45]

earlier today have to catch a class then told my mom to swap the battery and press the button.
later today, when I am flying during the last low pass, I heard some wired sound from the motor and decided to land on the next circle.
after one turn I feel the plane lost the power and I decided to turn head back immediately, and thanks to the wind today it soft-land on the edge of the crop，
no passenger has been hurt and the plane has not been damaged.

check the battery and only have 3.11v left for each cell
all my other batteries are perfect 3.75v
guess my mom pressed the wrong button.
lesson learned: always check the battery before fly, and never ask other person charges for u.

[SeeFernando]

Grab a few voltage alarms! 
https://www.amazon.ca/DROK-Accuracy-Detector-Pressure-0-5V-36V/dp/B00WQW4I9E/ref=sr_1_5?crid=15BLLB6DEO3AO&keywords=lipo+alarm&qid=1570986894&sprefix=lipo+alra%2Caps%2C175&sr=8-5

They're way cheaper on Ebay or AliExpress.

They've saved me when I've mis matched the C rating of the battery and the power draw of the plane.

[zhurui45]

Grab a few voltage alarms! 
https://www.amazon.ca/DROK-Accuracy-Detector-Pressure-0-5V-36V/dp/B00WQW4I9E/ref=sr_1_5?crid=15BLLB6DEO3AO&keywords=lipo+alarm&qid=1570986894&sprefix=lipo+alra%2Caps%2C175&sr=8-5

They're way cheaper on Ebay or AliExpress.

They've saved me when I've mis matched the C rating of the battery and the power draw of the plane.

I have one, just forget to use it.