I successfully used Kevin’s technique using a $5 1000 mAh battery pack purchased off of Amazon. I cut off the connector and soldered the wire ends to the metal tabs as described in his post. It took a while to figure out how to position the wires as there is not a lot of room for them under the batteries and they are both on the same side of the battery pack. I was eventually able to press the pack into the cavity deep enough so I could snap the LED board into place. Taped everything together tightly. After that, easy peasy.