I think (I could not find a clear description that was short and easy to understand, maybe I missed it) that it has a door on the box where the wood goes in, and a pipe that feeds fresh air into that box to keep the combustion going.
Did I get that right?
Batch box's purpose is to allow a more full-sized fire with the efficiency of a rocket stove, and there are several key differences to hit that:
- It should be made of a refractory material. Rocket stoves function perfectly well with plate metal or anything, really
- All dimensions, especially the air inlets and heat riser, must match a specific set of ratios to preserve the specific airflow needed to maximize burn efficiency. Too much means air will move too quickly, preventing full burn
- A choke point between the burn chamber and riser exists to slow down and funnel gasses and heat together. Without this, you don't have enough heat to get full combustion
Batch box burners tend to be quite a bit more fussy than a rocket stove to get going, though if a good portion of your exhaust rise is inside and pre-warmed, it should have a strong enough natural draft that starting it isn't much extra effort. I toyed around with the dimensions a bit myself and have something that works really well (cylindrical chamber rather than block), though I don't think I'm getting optimal efficiency out of it.