GoombaGeek: Your argument is kinda stupid.
The Dark Ages were centered on Europe, yes, but most fantasy is as well and, by the 15th century, Europe had caught up to the rest of the world and was one of the most highly "developed" areas.
And your argument about the lack of the Dark Ages or Renaissance doesn't make sense either. Toady said that technology would be limited to the 1400's. Were methods of extracting alkali metals known and used in that time frame?
And yes, batteries could have been made. Guess what? Hot air balloons could have been made by certain sedentary groups of Native Americans, and carts could have been made by Australopithecus. That doesn't mean that anyone ever thought to put things together in a way that probably didn't make sense at the time.
And where did I mention the Dark Ages, or Europe? I merely asked for evidence of alkali metal extraction by the cutoff date Toady has given. Not a system involving technologies they could have had and could have put together for a random reason and discovered worked--an actual example of such a system being found, or at least speculated on by an actual archaeologist.