if you're not even getting a static/crackle sound, the batteries may not be as good as you think.. my best bet is get a new sony wireless headset and try it in place. if that doesn't work, you can always return them. most likely the set your using has an old battery, even if it is reading 2.9v on the multimeter. try testing the current. not sure what it should be, but these batteries don't last for years, especially if they're not used much. just put an old JVC and a new Sony wireless headset in the same rack, the sony has about 5 times the battery life of the JVC that's just 2 years old.