This STRIX USB Power Adapter is a good solution for field charging the 1S cells that have a USB charger (it also charges my iPhone). The pass-thru XT-60 connectors provide connection for soldering irons & glue guns for field repairs that use 3S to 6S voltage.
The unit is basically a voltage monitor and display with volt/cell alarm settings at 3.7, 3.6, 3.5, and 3.4V. It also has a step-down converter to provide the 5V for the USB output.
To set the alarm voltage, press-hold the button on the charger until LED flashes and then tap button to cycle thru the 4 choices. When you have made your choice, wait about 10 seconds until the flashing LED becomes solid.
I checked the voltage monitor with a power supply. The alarm setting for 3.7V/cell produced a loud pulsing tone when the 3S pack voltage dropped below 11.1V (3x3.7V). A similar test at 3.4V/cell alarmed at 10.2V (3x3.4V).
Looks like it will be very useful!