Thats cool, what kind of vehicles were they in? The corrosion has to do with the grade of steel and amount/electrolyte of choice. The better the steal the more gas it produces with less electrolyte/ lower amps. A good system will need to be cleaned/flushed every 3-4 months where as a system w/ poor steel will be corroded in no time and need too much electrolyte to yeild a safe amperage.