Posted by David Sherman on Saturday, October 01, 2005 at 1:22AM :
In Reply to: CTD battery lifespan... posted by AAA on Wednesday, September 28, 2005 at 2:16PM :
I have revived many an abused battery by charging the heck out of it. Nowadays we tend to throw out any battery that gets sulphated, such as from being run all the way down. Modern "automatic" battery chargers are essentially constant-voltage chargers and won't fully charge a sulphated battery. Old books say a sulphated battery should be put on a 110 volt 5 amp constant-current charger for as much as 2 days, keeping the electrolyte topped up with water as needed. Far and away my favorite battery charger is an old 1930s army signal corps unit that is basically a transformer with a whole bunch of tap switches. I set it to whatever voltage it takes to put 5 amps into the battery, and then let it percolate away until the hydrometer says all the cells are charged. Often one "bad" cell will take twice as long to charge as all the others, but all that means is that the others will need a little more water added. I have too many rigs and too many batteries to pay $50-$100 for new batteries every time one of them won't hold a charge in the vehicle.
Some neighbor kids once turned on the light switch on my deuce, and by the next time I went to start it, months later, it was so dead that one of the batteries' polarity was reversed. New 6TLs are $130 apiece, and even decent Walmart batteries are $60, so I gave them both the 5 amp treatment for a couple days apiece, got the specific gravity up to the "good" range, though not like new, and have been using them for the past 2 years. They'll hold a charge for months and then start the truck instantly. I just doctored my M37 battery the same way and it appears to be thoroughly revived. This is also a reason why I quit buying any sort of "sealed" or "absorbed" batteries. I want to be able to overcharge them when necessary and add water.
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