There is a great LiPo circuit card with a digital display that will show how many cell the battery has (if it shows 3 S when it's a 4S one is burned out), shows voltage for each cell & total voltage. It's on ebay for under $10. See Lipo Battery Low Voltage Tester 1S-8S Buzzer Alarm, item#(180633061879).
THX, JIM
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