Posted by David Sherman on Sunday, October 02, 2005 at 1:29AM :
In Reply to: Re: CTD battery lifespan... posted by Jerry Henry on Saturday, October 01, 2005 at 1:37PM :
That seems like it would work simply because it would add more acid to the electrolyte. Running a current through epsom salt (magnesium sulphate) breaks it down into magnesium ions and sulphate ions. The magnesium reacts with water to produce magnesium hydroxide (milk of magnesia) which is insoluble in water and would settle to the bottom of the cells. The sulphate that remains forms sulphuric acid in water, raising the specific gravity of the electrolyte. You could achieve the same thing, however, and without generating milk of magnesia sludge, by charging the battery a good long time, checking the gravity of all the cells, and if any are still low, sucking out the electrolyte and adding new fresh strong electrolyte or even a bit of straight sulphuric acid. The reason why you can't always get the gravity of a cell up to what it should be is that some of the lead sulphate that forms in any discharged battery eventually ends up falling off the plates and settling to the bottom of the cells where the electricity can't get to it. Lead sulphate does not dissolve in water without the help of electricity and so it just sits there locking up both lead from the plates and sulphate from the acid. If there is still enough lead left on the plates to make the battery work, you can salvage the battery by adding more acid. I've yet to read a book that recommends this, but I've done it many times using sulphuric acid drain cleaner and it definitely does work. This is a last-ditch life extension or field expedient for a battery that you would otherwise be junking.