One develops a "feel" for flight time by keeping an accurate record of each flight, how the aircraft was flown, and what the battery voltage was when it was put on the charger along with the mA count of what went back into it when the charge cycle was done. Doesn't hurt to track the charge times as well. It requires additional time and effort to do all that but in the end you know what your batteries can safely do, you develop data that will permit you to instantly see when a problem is starting to arise, and you never crash you bird, AND camera, because you ran out of battery before your bird got back to where you wanted it to be.
How you fly it impacts flight time considerably. If you take off and hover for a full battery charge you'll be in the air a lot longer than if you took off and flew fast and hard. There is no "rule of thumb" here, everything comes from data developed over multiple flights to establish trends and averages. Some slap a voltage tattletale on their aircraft and wait for it to sound off before they go for a landing. A fair number of those people end up too far away to hear the alarm and end up with broken aircraft. The wise flyer learns what the batteries do under specific flight conditions and sets a flight timer that provides plenty of safety buffer to get the bird back home and on the ground even under heavy weight and aggressive flying conditions. You'll learn you can do 5 minute flights that consume more battery than a 10 minute flight, but you absolutely must perform the homework necessary to establish that data before trying to estimate flight times off of average mA consumptions. Remember than an average is derived from multiple data sets, not just a couple. The more data collected the more accurate the results, and the better the estimate.
What we do looks like a lot of fun and games to the casual observer but if your at all serious there's a lot of behind the scenes work that takes place to establish safe flying habits and a long lasting aircraft. Message here is don't put the cart ahead of the horse. Learn what you're doing before buying more advanced components. You just found out how understanding a battery can make a tremendous difference in flight time. You also tried to destroy a new battery on one of the first flights without realizing what you were doing to it. What you learn and do now will establish how much success you'll have with more advanced equipment. Without a good foundation you'll just end up spending a lot of money on stuff to replace what broke in the last crash. Those that have the most success learn to crawl before they walk, and walk long before they try to run.
