Heres a way to recharge batteries with water. http://www.youtube.com/watch?v=N0Et3R3mTMs (http://www.youtube.com/watch?v=N0Et3R3mTMs)
Thanks for the video's explaining how these water batteries work and showing what they can do. It might be old news for some and the technology might be considered basic and impractical to actually use, but I for one didn't know about it before and appreciate being shown how to put these things together. At least now I have the option of using this technology should I ever want or need to.
I think you might find that the magnesium will get consumed fairly quickly even using plain tap water. I have 3 cell made in a similiar manner that have been powering a red LED continuously for 14 months now on plain tap water. See this post:
http://www.overunity.com/9752/copper-zinc-tap-water-fuel-cell/msg257946/#msg257946 (http://www.overunity.com/9752/copper-zinc-tap-water-fuel-cell/msg257946/#msg257946)
I use conduit as the anode in these cells and conduit as scrap can be found for free. Even if you must purchase new, it is less than $2.00 for a 10 foot section.
I have not tried to charge batteries with this setup though. Even if a salt electrolyte was used for higher current, you cannot beat the cost for this setup. Not counting the copper, bottles, LED, or water: I have $0.19 invested in consumable materials for a light that exceeds 1 year of continous use.
Brad S