Personally I think we tend to over look the obvious. Why couldn't it simply have been something neat. A joke, a toy. "Hey Claudius...grab this." Of course the days of fun are long past but it had been known to happen.

My own personal view is that we're seeing an example of how technology can be lost and refound again. To quote a fictional example, nuBSG touched on the notion that certain things go out of knowledge, only to be rediscovered again. A piece of music, a technology, brought back into existence after once being lost. A sign of this is how many times the same thing has been invented at the same time by multiple people - the light bulb, the telephone, and we only remember the first one to get down to the patent office.

Earth batteries, such as the baghdad battery would function as, if treated correctly, can recharge, so if you had many of those batteries running together, so long as you never had to run at capacity, you could always be drawing power from some of them and not drawing from others, allowing them to recharge. Forgive me if my understanding of this process is crude, and if someone more educated than me can see a problem with this process, please correct me.

I then remembered something that I'd read in Job, and I found Job Ch 28 is talking about using the earth's resources, it's an interesting chapter. It mentions taking iron from the earth, and smelting copper from it's ore. The next sentence is "Man puts an end to the darkness" (NIV). Nobody's really sure who wrote Job, and since it talks in detail about the goings-on in God's "court", many believe it to be a work of fiction, a moral tale written about a figure either made up, or a story attributed to a known figure in order to pass on a moral lesson. However, it seems to be written from a contemporary stand point, Job being an "every-man" sort of character, it's descriptions of their lives are likely to be an accurate portayal of the culture at the time of writing.

If this knowledge was known then, the same principles inherent to nature were observed and utilised, man could have harnessed electricity by way of a copper rod put into the ground about a metre away from an iron rod. These sets of rods can be connected together, and with enough space, and enough rods, you could begin to build quite a considerable charge.

It made me wonder about the legendary Hanging Gardens of Babylon. Could they have been the perfect way to harness power from the earth in a way that improves the planet, rather than pollute it. You build an irrigated terraced garden system, with the terraces creating a power grid of isolated plots of earth, all inter-connected. Each terrace "cell" can then be taken on and offline, allowing you to toggle areas from charging and discharging. It becomes a sustainable source of free energy that also brings life in the form of trees, wildlife, an ecosystem.

Earthquakes apparently destroyed the gardens, but that knowledge would have lived on, for a time, and could well have led to the smaller, clay pot batteries, before the knowledge was lost, the clay pots ended up being used for some other purpose after they'd been stripped of their copper and iron.

Like I say, that's just my Friday afternoon's mind wanderings. I'mm not putting this forward as anything I can prove, it's just a possibility I came up with that sounds fascinating to me.