Is this a flare cartridge?

I found this in a garden in Eastern Europe. I broke it open to see what was inside of it. I have a theory that it is a flare cartridge from WWII. The inside of it has charcoal or gunpowder, I’m not sure which, and there is a central tube. Flare diagrams show that that tube would be the fuse. If it was a flare there should be a rim, but perhaps over the last 75 years it fell off or deteriorated. The soil here is very unforgiving. Iron nails are literally thin wisps of themselves after 80 years in the ground. So, if the rim or cover of the flare was metallic it may literally have disintegrated. Currently there is no metal in this object.The measuring tape in the pictures is in cm. I’m no ammunition expert. I don’t know if this is an old Soviet flare or if it is a firework or something else, but that’s why I turn to you, the experts.

Looks like a battery.

Exactly!

The outer case would be zink and has probably corroded away.

Good catch Sportclay, EOD, and Chickenthief. It appears to have been a zinc-carbon battery, however all the metalic features had completely corroded away! Thus, all that was left was this battery, shogun shell shape, filled with carbon powder and a carbon tube. The fact that all the metal had disappeared is what led me to initially discard the idea of a battery. I had read that batteries have up to 25% steel. This battery must have been in the ground a long time for the zinc outer case to have utterly disappeared, just leaving the inner substance of the battery and nothing else. Outer cases from zinc-carbon batteries, circa 1960, were made of cardboard, so probably this had a cardboard outer case with zinc used for the inner case.

Fertilizers, especially chemical, will cause rapid decomposition of the zinc and other metals especially if there are 2 or more dissimilar metals.

Thanks. I believe it.