The Futab BLS254 is stated to run on 4.8V. Ther is a lot of confusion on the net about wheter to use it only with 4.8V or up to 6.0V. Just one example here: http://www.helifreak.com/showthread.php?t=155974
But from my experience and many other guys you can savely go from 4.8 up to 6.0...