I totally forgot about these until I was cleaning out my office and found some old 6V lantern batteries lying around (garbage)
I'm guessing these were popular because it of their high capacities?
Early carbon-zinc cells had extraordinarily low capacity and gradually improved as the years went by. In, say, 1960, alkaline cells weren't readily available, and most carbon-zinc batteries (AA C D, 2-3 cells) paired with typical incandescent flashlight bulbs would deliver maybe 2 hours runtime. Even so, there would be a noticeable dropoff in light output after the first 30 minutes.
The 6v spring-terminal lantern batteries of the day used four F cells internally which had a nominal capacity about 1.5x four D cells. Because early carbon-zinc cells performed poorly with high drains (and the 500 ma lamps of the day were high enough drain to qualify) the F cells would outlast the D cells more than 1.5x. Early on they were used for taillights in cars where runtime was more important than portability. There were also electric railroad lanterns that typically used two of the 6v spring-terminal lantern battery that would last for an entire night; I would imagine that they used lamps that drew less than 500 ma but I can't find sources to confirm that.
But seems like every light out there that uses them are worth less than the battery itself? Were there any "good" lights/lanterns that used them, or did they come out at the same time as those molded plastic lights with the built in D handle? Also, I always thought it was funny that I've never seen a camp style lantern use a "lantern" battery
The spring-terminal batteries have been around a long time, I don't know, probably before the 1920s, in any case long before the molded plastick light. I believe the "lantern" nomenclature comes from their use in automotive tail lamps and railroad lanterns.
I guess I would say that I've never seen a higher-end or higher-performance light that used them. In the 1950s-1970s the higher performance lights would use the long rectangular screw-terminal lantern batteries that were roughly twice the size of the spring-terminal ones. I saw some 1970s ones that had sealed-beam light heads that performed fairly well for their day. It was also common for higher-end lights of the 1950s/1960s to use larger numbers of D cells rather than lantern batteries. I remember a family member having a long-throw light that ran on 7 D cells and had a reflector maybe 5" in diameter, for example.