One other thing to look at, is the power saving feature of the USB ports, on the system, as they might be powering down, when the unit is on battery power.
In the "Device Manager" you can right click the "USB Root Hub"(s), that show, and then select properties. On the power management tab, uncheck the box that allows the computer to turn off the USB port to save power (i.e. uncheck the box). Sometimes that has an impact on the connectivity of the devices.