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Typically, a large variety of aqueous solutions can be used in place of plain water. This battery type is specifically designed to pollute less (see environmentally friendly claims) due to the lesser use or the absence of heavy metals. Water-activated batteries have been used in radiosondes that shouldn't contain heavy metals since they regularly fall to the ground or ocean surface, and remain there indefinitely.
A carbon-magnesium battery, named NoPoPo, coming in AA size, was released in Japan in 2007. The batteries came with a syringe to inject water or electrolyte, such as juice. However these batteries have failed to make an impact due to their extreme low power output, very short active life-span and high cost. Moreover, due to the chemical reaction involving magnesium, these batteries are known to deform and cause damage to products used with these batteries. A water activated consumer battery called Aquacell is a carbon zinc battery with few heavy metals used in the cell. The battery weighs 12 grams and provides 1000 mAh on low drain applications. The overall latent pollution from the Aquacell life cycle is expected to be 4 - 5 x less than that of a standard alkaline battery.
Kits using copper-magnesium cells activated by water or the liquid sample itself are also in development. Another water-activated battery had been invented by Susume Suzuki of Total System Conductor. Aluminium anodes are used on many water-activated batteries designed for use with salt water such as seawater. The HydroPak uses water-activated disposable fuel cartridges as an alternative to lead acid battery packs and portable generators. It uses water added to sodium borohydride which releases hydrogen fuel for a proton exchange membrane fuel cell. It can be re-charged simply by replacing the fuel cartridge rather than the lengthy recharging that other batteries require, however the cartridges cost $20 each.