If there's anything less environmental sounding than battery fluid, we don't know what it is. Kids are trained to fear leaking batteries as angry anthrax-covered Aliens with especially acidic blood, but MIT scientists may have made the greenest battery yet entirely out of liquid. At least, according to them.
The new system is an fully liquid battery, a chemical cocktail which can contain charge and is even color coded. The batteries you know only have one liquid component, and still depend on a solid electrode - thereby limiting the scale of the system. With three liquids you can literally pour yourself a bigger battery, without any hardware bottlenecks - if your existing connections aren't good enough, pull them out and stick in better ones.
Professor Sadoway of MIT reports that the liquid cell can handle currents an order of magnitude greater than any other battery, are easier to make, will last longer and for only a third of the cost. Then again, he's only been reporting to the MIT-printed Technology Review so far.
In any event, a truly scalable and easily chargeable battery system could revolutionize green-power. A major problem in power production is simply storing the stuff from when it's plentiful for when it's in major demand. To supply a city, you'd need a huge field of liquid batteries to soak up all the juice, and where could you put them? Maybe under the huge field of solar panels providing the juice in the first place? Even without the eco-factors, easily storing electricity for any length of time without major losses is a system with guaranteed application.
More info @ MIT Liquid Battery