Some spade termination plugs were used to plug into the UPS's existing battery connectors, and female end connectors were used to plug onto the extra batteries. There is lots of wire slack in case it had to be moved around or if positioning in an enclosure were an issue. Short answer, it wasn't, an enclosure was not used.
Not shown in these first pictures, but observable below, there are four lead outs in total, not just three. There were some procrastination issues on finishing off the build in one weekend of just absently trimming wire leads and crimping ends.
Overall, the four battery rig will run my fluorescent overhead desk light for little under twenty four hours time. I hadn't been in the room for a while when I noticed the juice left out after testing. The original specs for the UPS indicate that it is designed to provide a late 90s / early 2000s computer power for about eight minutes, enough time to save documents and power it down. My light would require significantly less then that, but I do not think it lasted for more than six hours on just the one battery alone.
Nice little experiment, but I'll probably put the UPS back to only one battery and enclose it as manufactured. It works very well in a portable fashion when it can just be unplugged from the wall and carried around. While it will only supply 3W of power, that's more than enough for phone chargers, lights, or the like.
