Last post, I checked out the UBEC as a DC-DC converter to power the Raspberry Pi 2-B from a Ryobi 18 V tool battery. This time, I actually plugged the RPi into the battery power. I attached the 5V output leads to a USB socket so the RPi could be powered through the micro USB connector for additional protection.
So far, I have operated the RPi2 from the battery for over 8 hours, including working on the Apache server (see later) over SSH, and an HDMI connection to a TV part of the time. Battery open-circuit voltage dropped from ~22V to 17.35V. Looks promising so far. I’m planning a battery monitor using one of the channels of the MCP3008 analog-digital converter for a more accurate measurement of power status.