WiFi mode uses significantly more power than flight mode and will drain the Mercury's battery quickly. The device is designed to enter WiFi mode only when connected to a USB power cable, which ensures the USB power runs the WiFi radio rather than drawing from the battery.
Forcing WiFi mode without USB
If you're stuck without a USB cable and need to upload a flight to the Altimeter Cloud or change your settings, you can force WiFi mode to run from the battery for up to 3 minutes.
To do this, hold down the BUTTON (not the power button) for 7 seconds while in flight mode. WiFi mode will be enabled for 3 minutes.
Warning: This puts significant strain on the small LiPo battery. Running WiFi from the battery will completely drain it in just 15 to 20 minutes from a full charge. If your battery is below 50% there may not be enough power to force WiFi mode at all. We recommend avoiding this option where possible and remembering to bring a USB cable.
Press the power button to turn your device off once you are done to conserve your battery and exit WiFi mode.