It’s worth checking to see if the transmission LED on the underside of the Vue ISS is flashing unexpectedly. This LED is designed to start flashing after you’re pressed the channel selection button/transmission test button. But it should stop automatically after some minutes and remain off unless/until the button is pressed again. If it hasn’t stopped (or has restarted of its own accord - which can happen under some circumstances) then the battery will have only a relatively short life because of the extra battery drain caused by the flashing LED.
Let us know if the LED is flashing unexpectedly - there is a simple fix that may work.