Sorry, but this battery thing is a bit over the top for me. It seems a lot of people can't be satisfied with any amount of flight time they can obtain from a battery and are on a life long quest for the "magical" 2 hour flight time battery. Whether the stock Yuneec battery is a 5400mA or 6300mA really doesn't matter. We might presume it's 6300mA as the flight time it provides pretty much equates across the board with what all the other 6300mA batteries provide in flight time. Sure, there are minor difference of a couple minutes either way on an average but the conditions and the way those batteries were flown established the flight time they delivered. I sort of look at it like the gas tank in my car. I hasn't mattered a twit which brand of gas I've used, that tank provides ~400 miles of range, with some variation dependent on how I was driving, regardless of the brand or grade used.
So we have the Yuneec batteries that deliver "X" flight time, with that amount of time a variable impacted by weather conditions and how aggressive the operator flew their H. We have the Tattu batteries that deliver almost exactly the same flight, and re-charge times and mA inputs for virtually the same about of flight time for ~$70.00 to $80.00 less than the Yuneec batteries. Both the Tattu/UltraX and Yuneec batteries for the most part hold up for a long time if they are treated as they should be treated. All of mine are now over a year old and the only ones that have gone bad were all over discharged. We see the Venom batteries listed as having 400mA more capacity than the Tattu.Ultrax but at $60.00 higher price per battery. Then we have the exalted 8000mA GiFi battery that some have tried, and found not to their liking. Graphene batteries have worked for a few more minutes of flight but some have reported relatively short battery life spans. How much is a couple extra minutes of flight time worth to you?
There's no reason to be tense while flying because of battery state. It's too easy to periodically look at the battery level while flying. It doesn't take all that many flights to determine what your average flight time will be, and there's no reason to fly to the other end of the earth during the period of time you are learning how much flight time you might expect. Those that use a little bit of intelligence invest in better chargers and monitor battery conditions, noting voltages before and after charging and recording mA inputs for each battery. Other buy better charges and log their flight time, along with end of flight battery voltages and track all of that and compare mA input for longer flights in order to establish the lowest safe voltage they can fly to. They understand that lithium batteries should not be flown down to more than 70% capacity, with capacity being the charge state in mA. A 6300mA battery should not be drawn down more than ~4410ma, and at that level the battery will be at a specific voltage. This is where the Yuneec battery is a bit of a quandary because it states it's a 5400 mA battery, but if you treat it like a 6300mA battery it still keeps on ticking like it's a 6300mA battery. A 5400mA battery would have died an early death if treated like a 6300mA battery. Those that fly like a bat out of **** learn that doing so causes the battery to generate low voltage warnings fairly soon because the load on the battery can exceed the burst discharge ability and cause voltage to temporarily drop below the warning level. Reducing the electrical load permits the voltage to creep up again after a few moments, but that doesn't mean flight time just got extended. All the current used in that wild flying is gone and it's not coming back after you relax thumb pressure. None of this stuff is rocket science.
My first Pro level camera rig was a Cinestar 1000mm 8 with a FreeFly Radian Gimbal fitted with Canon and Nikon cameras, and could carry a Red. It required a pair of 6s batteries, generally of 7,000mA to 12,000mA capacities. On a good day with the lighter Canon or Nikon and 14,000mA of batteries it could fly for 7 minutes. If the wind was blowing pretty good that reduced. The rule was to always be on the ground, or on the way to the ground by the 5 minute mark. With heavier cameras and the 20,000mA of battery capacity the flight time was pretty much the same. We got used to it and planned our flights around that flight time. People would have just about killed for 10 minutes of flight time back then. Since then flight times have gotten better because of more efficient components and lower aircraft/camera weights. There have not been any earth shattering breakthroughs in battery technology, and energy density has not improved all that much in the chemistries available to us. Battery prices have gotten a lot better though.
I guess is to simply accept what is. Plan the flight, fly the plan. if you need 1/2 and hour of flight time you're either flying much too far away or flitting about trying to figure out what to do. Buy a few extra batteries. You really didn't go into this stuff because it was cheap, right?