When I got my Burgess Safari Lite 6 years ago, my ultimate goal was to someday find a way to run it portably again, as the original 69V batteries it uses have been extinct for decades. My original plan was to use ~35 Li-Ion cells in series to get the required voltage, but I ultimately decided that was too dangerous and cumbersome.
Recently I bought a DC-DC converter on eBay that can be adjusted to output up to 390V. I set the output to 115V (for a happy medium between lamp power and converter efficiency) and wired it to the Safari Lite's battery terminals, and it works a treat! It's powered by a three cell Li-Ion battery pack, and it's all stuffed inside the battery compartment. With crappy 600 mAh cells, I can get a runtime of an hour and a half on low brightness. The DC-DC converter is nice because when the input voltage begins dipping, it lowers the output voltage to compensate, giving an effect much like as if the lantern were running straight from batteries.
The only caveat is that I had to add a secondary power switch for the converter, since it has a quite high quiescent current. If I knew how to disassemble the lantern, I could have possibly wired the converter through the AC/battery switch, but oh well.
I recall years ago someone here told me that a fluorescent lamp's current rating is derated when running on DC current, because of the extra loading on the cathode compared to the same level of AC current. I forget what that value is now. The lamp current is 0.10A with the 115V output, so I assume that's okay.