Nickel-cadmium vs. sealed lead-acid

"Any battery will get warm and has the potential for thermal runaway. The runaway, he explains is a result of a cycle where the battery shorts internally, the voltage in the battery begins to drop, and the charging system increases the current — this becomes a viscous cycle. With Ni-Cads, the substrate material on the plates is generally steel or pure nickel, and when they weld themselves together, there is no melting apart and the short becomes more severe. As that heat builds up, another cell adjacent to the shorted cell will have a failure of its separator and they also will weld themselves together and the current building up just feeds that short. With a lead-acid battery, however, the plates are made of pure lead, and so when they short and the current builds, the lead melts before it does any substantial damage," he says.

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