Originally Posted by Raspy
Deep cycle batteries will always have less amp-hours than starting batteries for a given case size because they leave space in the bottom below the plates to accumulate the old lead or products from becoming sulfated. Batteries die when this material builds up and shorts out the plates. So deep cycle batteries can take abuse longer.
Actually, deep cycle batteries, for a given group size, have more amp hours and less cranking amps. The reverse is true of starting batteries.
Deep cycle and starting batteries are designed for different purposes. The deep cycle battery
is designed to provide electrical
current at relatively low amperage over a long period of time before recharging and to stand up to frequent charging cycles. Starting batteries are designed to provide the large instantaneous amperage required to turn over an engine
Without getting into all the chemistry, the difference basically boils down to surface area and plate thickness.
The more electrolyte that is in contact with the plates, be more amperage the battery
can produce. Conversely the less electrolyte in contact with the plates the less amperage produced.
Thicker plates are necessary to provide the high cycling(charging cycles) capacity required in deep cycle usage. Thicker plates means fewer plates in a given BCI group size, therefore the battery will produce less cranking amps, but can provide current over a longer period of time(amp hours), as electrolyte is depleted slowly.
Starting requires instantaneous amperage, and that requires more surface area. Consequently, the plates need to be thinner to provide the surface area needed in a given group size to provide this higher amperage. Electrolyte is depleted rapidly in during this high current production. As a result, the battery will need to be charged sooner.
Sulfation is an internal chemical process, not to be confused with terminal corrosion.
All batteries, as they discharge, produce lead sulfate. The process actually begins as soon as the battery is taken off of the charger. However, the lead sulfate crystals produced during discharge are very small and are converted back to lead during the charging cycle.
In common usage sulfation refers to lead sulfate forming large crystals which cannot be readily converted back to lead by charging, and usually means the battery will have to be replaced. This type of sulfation takes place when a battery is left in a low state of charge for a long period of time.
All batteries have space in the bottom to accommodate the normal products of the charge\discharge cycles which accumulate over time.