"Dry Cell" is a common name for a particular design of hydrogen electrolyzer, or HHO generator. The name sometimes confuses people because it still uses electrolyte in water like any other electrolyzer.
But it has some properties that make it a better design, and we will
show you how these properties could bring about the name of "dry cell".
Perhaps a better name could have been found for this design, but it's
pretty clear that the name is here to stay.

With the dry cell design, the whole cell is not submerged into an open bath of electrolyte as all other common types of HHO generator are. Instead, the dry cell's
plates are separated by rubber (or similar material) gaskets, and the
electrolyte is confined inside those gaskets. The edges of the plates,
including all of the electrical connections are outside of the
electrolyte bath. Here is an image of one of our cells that will help
illustrate this.

You can see the edges of the plates between the black gaskets. What is not so clear in this picture is how the electrical connections to the plates are also outside of the electrolyte
bath. But they are. Tabs on the plates are used to make the electrical
connections. These are the only parts that are dry, and rightly or
wrongly, give the dry cell its name.

So to summarize, the points that make a design a "dry cell", are that the edges of the plates and the electrical connections to the plates are dry, or are outside of
the electrolyte bath. That's basically all there is to it.

Some Advantages Of A Dry Cell

There are 2 main reasons:

1. When the edges of the plates are submerged in the electrolyte a great deal of the electrical current passes from the edges of the plates. This current is
   largely wasted in terms of HHO production. When the edges are outside of
   the bath, all of the current is forced to travel from the faces of the
   plates. Therefore all of the current used is utilized in efficiently
   making HHO gas. This is the main reason the dry cell design has caught
   on so thoroughly.
   
2. When the electrical connections are submerged in the electrolyte bath, the electrolyte attacks them and will eventually destroy them. The plates of dry cells are common made of 316L
   stainless steel (some use SS317L ,Inconel 625 alloy,Ni201& Titanium and some use MMO coating Ti) . This has been found to have the good properties of
   resistance to attack from the electrolyte while still giving adequate
   electrical conductance. However, mounting hardware and wire and cable
   are very difficult to find in this material, and they are cost
   prohibitive to use. Therefore copper cable is usually used and a lower
   grade stainless steel nuts and bolts, and when these are submerged in
   the electrolyte, they rapidly get eaten away. With the dry cell design,
   all of these connections are outside of the electrolyte so this isn't an
   issue.

Summary

So that's a "Dry Cell". It is a very simple concept. There are still a great many variations in this design from manufacturer to manufacturer. Number of plates, how the
plates are powered, and how much voltage is applied from plate to plate,
are just some of the parameters that can vary. But if they are dry
cells they have the qualities described in this article.