"All that is required is a small  supply of a sugary drink... Bio-batteries are fully biodegradable  and have, on a single charge, a potential life-span three to four times  longer than conventional lithium  batteries." When someone sees a quote like this, that too on a  reliable news aggregator like Google, it's hard to just move on and  click 'next'. According to a report in CRN.com.au, a paper on a Coca  Cola-powered mobile phone was  recently published by Chinese designer Daizi Zheng, the aforementioned  quoter. Basically, as a part of an Eco project, the designer used the  sweet soda to power a mobile phone. The claims are impressive and say  that the battery can last 4 times longer, and is fully biodegradable.
 
 
 
My  take on this is simple: I don't think Coke wants to be known as a  battery fluid, as i do remember my 8 th standard Physics clearly-  battery fluid is strongly acidic. There have been reports that Coke has  been used as an industrial cleaner, and for that matter any of the colas  can be used for that due to its phosphoric acid content. But going  further into the battery topic, the efficiency of this battery is  questionable, and also safety of the use of an alternative electrolyte  like Coke. There is a chance of it reacting wrongly and even exploding.  To nullify this in commercial production, the R&D costs go up. 
Recharging  means buying a new Coke can, so it's no doubt cheap in theory, but mass  production of the battery itself will be expensive. There are other  sources of BioFuel like edible foods such as edible oil seeds, Corn and  Jatropha. 
But Bio batteries are not all  theory. None other than Sony has been toying around, literally, with the  concept of Bio batteries. Geek.com very recently covered a report on  toys that use few drops of sugar filled liquid to power its small toys,  batteries provided by Sony. "Such batteries run on just a few drops of  sugar solution making them an ideal and safe replacement for batteries  in children’s toys."
On further web browsing I  stumbled upon an article on how to make  your own Bio battery, thus it's not really a heavy commercial  process, DIY dudes can surely check this one out.