Other problems with the FX5 that you might run into but this is how to fix it.
Never use less the mAh 2400 rechargeable batteries in the FX5.
Also use the regular Foxpro Battery Charger that you have to plug into a electrical outlet.. The Quick charge FP charger that you can use in a car lighter with the attachment that can also charge in an electrical outlet just does not charge the batteries like the regular FP charger you plug into an outlet... Also Some of the charger that come with Rechargeable batteries that you plug into an outlet are also excellent for recharging AA batteries for the FX5.
Hang the FX5 in a bush or tree, place it on a bale of hay, hang it off the ground...It works better..
If the antenna gets pinched behind a branch the remote will not work well.. Make sure it standing up and not covered while hanging in a bush or leaves..
When I first paid the bucks for my FX5 I even said to myself? What did I go and buy this for..However stumbling on things I mentioned above corrected many of the problems I was having with my unit...It is a good quality caller...
I know you were having a true tech problem... However I figure I pass on things to others that might be having a set back that is really not a set back with their FX5.