An engineer friend, Chris Moller, has a passion for a particular region of Africa and spends a lot of his spare time on development trips there advising on sustainable power technologies. One of the problems facing the developing world in its aspiration to come up to our "standard" of living is that while there is plenty of sun in most places, converting it into storable electricity is a real problem. Lead-acid vehicle batteries are one solution to the problem, but these require maintenance, topping up sulphuric acid and they wear out as lead sulfate deposits form within. Needless to say there are mountains of dead car batteries accumulating across the continent going to waste and causing environmental problems.
Nevertheless, Moller tells me, individuals will push wheelbarrow-loads of discharged batteries several miles to the nearest town to have them recharged for a fee and then push them back to the village where they are used for lighting, in schools, homes, local medical centres, and even for charging up mobile phones. It was with interest that he learned of a possible chemical alternative to sulfuric acid that might allow old car batteries to be re-used with a safer, less corrosive chemical, alum solution, apparently. Moreover, this supposedly makes them more suitable for use with solar panels in that they can survive a deeper discharge.
A quick search on the web reveals that lots of people are talking about the possibilty of rejuvenating lead batteries. If it were viable it could kickstart a cottage industry in sub-Saharan Africa for carrying out conversions and supplying the raw material as a much more viable battery than lithium-ion rechargeables with their very limited lifetimes in hot climes.
My gut feeling was that a lead-acid battery, by virtue of its name requires an acidic electrolyte. Although they are nineteenth century technology they remain viable and reliable, despite the need for toxic lead. Two identical lead plates with a coating of sulfate are separated by the electrically conducting acid solution (usually stronger than 4 molar sulfuric acid), often held within a non-spill gel in modern car batteries. Charging involves water reacting with the positive plate to form a lead oxide layer and releasing hydrogensulfate, hydrogen ions and electrons. These latter two react at the negative plate to produce metallic lead and release more hydrogensulfate. Discharge then involves the conversion of both plates back to lead sulfate with the release of hydrogen ions and electrons to generate a current.
The alum solution would contain hydrated potassium aluminium sulfate (potassium alum), for instance, would supposedly convert a lead-acid car battery to a lead-alkali car battery. There are lots of people on the web who claim that this works and they offer "how-tos", recipes and other discussions where they claim to get their rejuvenated battery up to 6 or 7 volts. However, my searching seems to point to a single post on the net about 6 years ago. Unfortunately, the page also discusses the ludicrous notion of cold fusion, bizarre alternative health foods and several other unproven conjectures.
A full literature search on my behalf by chemist Robert Slinn raised nothing of any merit to the concept. Electrochemist contact Phillip Cook also had this to say: "Everything that I've found makes me very skeptical. Most of the evidence of the viability of these alum conversions seems to be found in sketchy YouTube videos. I have yet to find a proposal of a viable electrochemical mechanism," he says.
Unfortunately for Moller and his African contacts, it seems that this is yet another example of fantasists hoping to find a kind of cure-all, some kind of energy panacea. The general discussions are not dissimilar to the almost religious ferocity with which those who claim to have found perpetual motion talk about oil company conspiracies.
There is one final clue. Apparently, car mechanics have been known to use Epsom salts as a cleaning agent for car batteries, they remove some of the deposits, the mechanic can top up the battery with acid, and recharges it and that old lemon on the forecourt that wouldn't sell will see some sucker drive it away at a bargain price only to have it fail on them a couple of weeks later...
David Bradley blogs at http://www.sciencebase.com and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".