This article is from the Radio Control (R/C) Flying FAQ, by Shamim Mohamed firstname.lastname@example.org with numerous contributions by others.
Modern NiCd batteries are pretty amazing. You can charge them in 15
minutes, take power out of them at up to 50 amps or so, and do it all day.
That capability is what makes electric flight possible. Electric power can
be used for any kind of flying---gliders, aerobatics, even racing. It's an
excellent choice for sport flying.