Fernando,
Battery prices may appear to be quite expensive but when compared to a regular IC engine set up, they are about the same. (or cheaper) When I fly one of my .60 size stunters with IC power, I burn about one dollars worth of fuel per flight.
Last year each of my Thunderpower 5S2P 4200 Pro Lite batteries cost me about $300.00. They are now down to $230.00 each. I expect to get around 250 to 300 cycles from each of my batteries. That's already cheaper than using glo fuel.
There is no denying that the cost of the support equipment (chargers, balancers, monitoring and test equipment) is not small and is not really an optional expense when dealing with large batteries.
As to the technology, we need batteries that have very high energy density and very high "C" ratings (the ability to dump the charge out fast) while also being lite in weight, small in size and safe. While some have in fact used electric drill motors and batteries in the R/C world, I do not think that would be successful approach with control line.
Construction of my plane SHOCKWAVE began just over a year ago. Just eight months earlier the decision to build it would have been a definite no. It was the announcement of the Thunderpower ProLite series of batteries that made it possible. Technology is changing rapidly and prices are comming down. I do not think you will see a $50.00 battery that will power a large stunter for three hundred flights in the near future but I also do not think that present prices are out of line with the alternatives available.
Kim.