Replace the battery and the antenna, and update the firmware.
Battery and antenna are available off Amazon and it takes about 10 min per collar.
That's easy for you to say.
It really is that quick. Remove the collar, remove three or four small screws, unplug the battery with the help of a very small screwdriver, do the same with the other connector, one more tiny screw to remove the battery holder, stick the new battery back in (with the end spacer from the old battery), replace the battery holder and that tiny screw.
IMHO, The most important part comes next and it's not found in on any of the online videos. Carefully remove the o-ring. Clean it with alcohol and clean both mating surfaces. Lubricate the o-ring with the just a little silicone grease and replace. Then you are ready to stuff the wires back in, plug the battery back in, then put the screws in. Take are not to overtorque the screws
Once you know what's inside, it really only takes about 10 min...but going slow the first time makes a lot of sense.
The antenna connection is under a different cover, but is pretty quick.
I never said updating firmware takes only 10 min. That was a pain, but did seem to address an issue with re-acquiring the collar.