You may be talking about a different 80%. Since OP is talking about flight duration, that is mah related, miliamp hour. Not voltage. Op also mentioned he flew for less than 3 min, and put in 2091mah. I’m going to pretend he flew 2.5min and used 2091mah. He needs 836.4mah per min. With his 5000mah lipo, he should be able to safely fly 4min and 45 seconds. That’s the 80 percent rule OP is referring to . Setting the alarm at 3.7/3.8v is too high, there are plenty more usable capacity left as evident by OP just putting in 2091mah per flight. And a less than 3 min flight is way too short for a “normal” set up.
Thank you for the amazing responses.
Seems I understood the 80 percent rule wrong.
What i do now is this. I set the battery buzzer to 3.6 as a pre warning and then the fail safe and warning at 3.5.
Going to do some tests today and see what that gives me. Pretty calm day as well
Bigger lipo battery can be powered more energy. In fact As the battery gets larger, the increase in flight time becomes ineffective. For 450mm fpv not need purchase 5000mah battery, 4s, 3300-3600mah it’s ok. Formula flight time =(Battery Capacity * Battery Discharge /Average Amp Draw)*60 (From http://www.rcdronegood.com/quadcopter-battery-calculator-flight-times/) There are 3 main factors: Battery Capacity , Battery Discharge and Average Amp Draw. therefore you should choose 3300mah with hight C 75C or more. Hope can help you.