The LT1 can be ordered with a set of 3000 mAh cells. They are nothing special, but they are not bad either.
If you want 16% more runtime, you could get a set of four Samsung 35E 18650 cells with button tops.
To ensure there are no fires, measure the voltage of each cell with a multimeter. Make sure they have the same voltage, at least within 0.05V of each other. Then put them into the light, with the “-” end on the springs and the “+” end up. Close the lantern. Afterward, treat them as a married set, and charge them by plugging the lantern in to USB.
Or just use the cells Sofirn ships with the light. They’re pretty decent.
If your room has a white ceiling though, it may be more effective to use a traditional flashlight instead, and shine it at the ceiling. This distributes light more evenly, and reduces glare, so it’s easier on the eyes. And, of course, if you need to see something up close in detail, move or aim the light to point at what you are doing.
The traditional forward-facing light which most closely matches the LT1 is called a Q8. Some versions of it have built-in charging. However, it has a much much brighter high mode, so you would need to run it much closer to the bottom of its range if you want it to last 25 hours.
Another option is to use a smaller light at a lower brightness level, and simply aim it at what you want to see. This gets the same runtime and the same or better visibility, for a lower cost. Some “angle lights” can even be clipped on and worn as clothing, to see in front of you no matter where you are.
This curated list shows what’s good at the moment.