Mike,
I fly RC airplanes and we constantly make our own battery pacs....as long as they are put in a heat skrink sleeve, shaped to the correct configeration to go in the device and all jumpers are soldered onto the batteries after the heat shrinking step, charged and cycled properly you shouldn't have any trouble,,,,,I have flown 35 and 40 lbs planes,,,mostly 1/4 scale,,,,,and at 40 to 80mph,,,,you want them to hold up. Tower Hobby has a good selection of different size batteries to make these packs. other suppliers should have as well....I had to trust my batteries due to the dangers of flying a plane in close proximity to spectatars. As for the purpose its used for I guess each has to weigh that to determine its value,,,,but batteries are just batteries afterall