I ran into a problem last week trying to run with USB power and not battery. I've been running this way for months connected either to a USB3 port or to a USB2.0 hub with a power supply. What I found is that I switched USB cables and evidently the cable (was a super cheap one on eBay) can't handle the current draw of the Modem. After it dawned on me that I'd switched the cable I returned to the cable that had been working and all is well again. I've had similar problems with other development boards where some USB cables can't handle the load. Thought I'd post this in case someone else runs into problems running without a battery as it might just be the USB cable.