With two sets it takes me about 4-5 hours to get in six practice flights. That time has gotten a bit shorter lately due to the fact that I'm not taking as much as I used to out of the batteries... but it was a good rule of thumb. With three sets that time could have been cut almost in half. Time isn't that big of a constraint for me, so that's why I have only two. I do have a third set now actually, but it's a different battery than I have been using and plan on testing it to see if I want to go that direction.

As for charging the batteries, I have two Astro Flight 109 chargers that cost about $130 a piece retail... and I use a 12V Deep Cycle battery bought at Costco for about $50. Others use portable generators and power supplys. Very nice set ups, but it ups the cost considerably. I can buy another set of batteries for what the gen would cost!

What does need to be said though... is if you are going to get into electrics you have to do your homework! Find sombody who had good luck with them and ask them questions, watch what they do, and model your set up after theirs if at all possible. If you don't have anybody out there who flies electric, ask your questions on here... It may not be the most expensive way to go, but it can get there quickly if you make a mistake and fry a battery. These things aren't like the nicads we used to use on R/C cars or boats, you can't abuse them... You must make every effort to take care of them and monitor them.

Steve and Chad are absolutely right about time. Figure a shelf life of about 2 years... whether you fly them or not they aren't going to last much longer than two years, and you might as well get your money out of them right? Four sets at your fingertips doesn't do you much good if you only get 25 cycles a year on them each... you are just wasting money at that point as Chad pointed out.