Here is great article, read it. It has some useful tips to extend your drone battery life. Google is your friend ;);)
www.fitdrones.com/how-to-extend-drone-battery-life-and-have-more-fun/
3-5 hrs?? No way with this technology, maybe in 5-10 years that will be possible. Army probably have that technology, but ordinary people still doesn't have that privilege. You should read some articles how to expand your battery life.