Nuts & Volts - February 2006

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with frequent charging. If the battery sits for a while unused, the sulfates dig deeper into the plate. This renders that part of the plate useless because it can’t conduct current as readily as a clean plate. Fortunately, this layer can be recovered by keeping the battery on a trickle charge. If left too long, though, the sulfate will eventually go into what’s called level 3 penetration, where the plate is worthless as a conductor (sulfur is an insulator) and normally not reversible. So, you tell me. Has this battery been sitting for so long that the sulfate has progressed to level 3 — stage 4 cancer? If it’s at a level 1, put the battery on a trickle charge. If it’s at level 2, put it on a trickle charge for longer. If it’s at level 3, try my pulsing charger and hope for the best.

What are the chances of bringing a dead car battery back to life? Zip to zilch. Car batteries have calcium-lead plates, which provide a large amount of current for short periods, but have little endurance. Think of the car battery as a Cheetah — a very fast cat with a huge burst of speed, but can’t complete a marathon. The plates are

large in area, but very thin and very subject to shedding when deeply discharged. In fact, a car battery should never be discharged below 90% of total capacity. Doing so quickly depletes the lead paste in the plates.

Did I mention that deep discharge doesn’t have to come from use? It can also come from just having the battery sit on a shelf (or under the hood unused). A battery has impuri-ties in the electrolyte that causes cur-

rent to flow within the battery proper between the positive and negative plates. A rule of thumb, this amounts to 10% per month. (But don’t quote me on that. It depends on the battery itself.) So after 10 months, the battery could spend all its energy internally and have sulfated to the point where it may never accept a charge simply because there’s no conductive surface left. You can try pulsing the battery, but don’t hold your breath. NV

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