I have not had a problem of range with the 6100 in a 48"ws electric.  I don't fly it to the extremes of my vision.  Are these used? If they were purchased within the last year they should be OK.  If they are older they may have the long reboot time (4 seconds); the newer ones reboot in 1.5 seconds I'm told.  I sent in all my old ones for replacement two years ago.  If you can't document when they were purchased, Horizon may not replace them for free.