What are the differences between a starting and deep cycle battery?
Generally speaking there are two different types of lead acid battery, Starting and Deep Cycle. If a starting battery is routinely deep cycled (discharged below 20%-50% of max capacity) it will generally fail after 30-150 cycles. The same starting battery will last for thousands of cycles if it is just used normally (2% - 5% discharge).
A starting battery is generally designed to start some form of internal combustion engine (car, truck, boat etc). In a starting battery you will find more lead plates, thinner and often made of a lead "sponge" similar looking to a foam sponge. This sort of arrangement means that the plates have much more surface are in the solution than a Deep Cycle battery and allow them to draw larger currents much quicker than a Deep Cycle battery.
A deep cycle battery on the other hand has much thicker plates and they are solid, not sponge. These thicker plates have less surface area and thus less of the instant power that a starting battery needs. They are designed to be discharged down to 20% of their maximum charge repetitively. The thicker lead plates allow for this as they are much sturdier than their sponge counterparts.
Cold Cranking Amps (CCA) is an indicator of the amount of current a battery can deliver for 30 seconds at zero degrees Fahrenheit without dropping below a specified cutoff voltage (normally 10.5 volts). The cranking amps a battery can produce changes with temperature. The warmer it is the more Cranking Amps a battery will produce.
You can use a Deep Cycle battery as a starting battery provided that you take into account the lower CCA of a Deep Cycle battery. As a rule of thumb it's a good idea to upsize the battery by about 20% to deliver the same amount of cranking amps from a deep cycle battery. Also the self discharge rate of Sealed batteries is a lot less than flooded lead acid types.