Backstory: For about a year now i have been designing and building long endurance prototype electric paramotors for an established paramotor manufacturer. About a month ago i had two types of li-ion cells that i needed to compare with each other and test at fairly high current. So to compare the 21700 cells, i made two 4s1p battery packs for my drone because of the ability to monitor current, mah used, voltage sag, and all that good stuff. I was quite surprised to find that i could easily get 23 minutes from both batteries from a drone built for bashing/racing. I then made a 4s2p battery and was even more surprised when the drone flew 32 minutes! So long story short: I got hooked on endurance drones.

(updated 2/22/2021)
My current best flight is 45 minutes with 2s sony vtc6 battery and a 195 gram all up weight. I have been busy with other projects so I haven't done any other endurance flights. Projected flight time is 49 minutes 15 seconds with my 2s 3500mah samsung 35E battery pack and 55 minutes 40 seconds with my 2s 5000mah tesla model 3 21700 battery. My first calculations put this drone at getting closer to 70 minutes of flight time, but due to some silly mistakes in my math the dji mini 2 motors are about 25% less efficient than I had calculated.

This drone is ridiculously efficient. Full throttle is 12 amps with a 2s battery. This equates to about 90 watts of power which is about half the power it takes a typical 5" quad just to hover! The hover power on this quad is as low as 16.65 watts with my lightest battery which is less than 1/10 the power a typical 5" fpv quad uses. I also find it quite enjoyable to fly as it is VERY quiet(You can't hear it hover from 50 feet away) so I am not woried about flying it around my house and bothering neigbors, When flying it around my house the AUW is only about 130 grams so the chance of it seriously injuring anyone or damaging property is nearly zero which helps me relax and enjoy it a bit more, it turns on a dime, it can fly seemingly forever which I have come to enjoy(i still regularly get 8 minutes out of an old 2s 300mah battery. yes you heard right 300mah!), the thrust to weight ratio is almost 6:1 with a small battery so it isn't slow, the motor idle rpm is so rediculously low that it has close to the same float as my regular 5" quad, and it still has the performance to powerloop 30 foot trees.

*update #1: I recently did my first endurance test flight. I "only" got 45 minutes and 5 seconds running the 2s 3100mah VTC6 battery pack down to 6 volts. I would have gone lower as a typical li-ion is rated to go down to 2.5v/cell but my 4-in-1 esc system has a 12v regulator which makes the quad freak out at 6v. So I am looking into a whoop flight controllerI/ESC that can handle 1-2s lipo which should give me the working voltages I need to do endurance with a 2s Li-ion. In the meantime I am making a 3s samsung 35E battery pack which should bring my flight times to about 55 minutes and will allow for a 100% battery discharge.

*Update #2 12/21/2020: I finally got the camera mounted. I ended up using two modified zip ties. the weight is now 95 grams with the battery strap. I also found the weight to be 82 grams without the top plate or camera. I did need to replace a motor which is why I haven't done any more endurance flights so I hope testing to continue tomorrow.

*update #3 2/22/2021: I plan to try going solar soon. I have found a combination of solar panels that will weight under 110 grams and a support system should weigh under 40 grams which should be a low enough weight to keep this drone under 250 grams AUW. the planned solar aray will be 2.8 square feet and provide an average real world power output of 48 watts and a peak output of 56 watts which should be more than enough as this drone hovers at 35 watts of power when loaded to 250 grams AUW.