Dual Purpose Batteries
Many different batteries can have more than one use. For example a wet cell starting battery might have 900CCA because of its high acid concentration. It will also have a reasonable amount of active material to produce that power. It's not designed for cyclic applications but that doesn't mean it could be used 40-50 times to 50% depth of discharge before the batteries active material deteriorates.
The other end of the scale is a large 8D 12 volt 260Ah battery could primarily be designed to provide low current discharge over a 20 hour period and be able to do that 800-1000+ times. These would be considered deep cycle batteries and have a good usable life of a few years if you discharged them daily to 50% depth of discharge. Where if you had a battery that was referred to as deep cycle but it only has 400 cycles to 50% depth of discharge it might be called deep cycle but on comparision will only last half as long if cycled daily as an 800 cycle battery.
Adding to the dual purpose conundrum is a large 260Ah battery still has a lot of active material and while the acid concentration isn't high like in a cranking battery (so it will have a lower energy density) the battery will still be able to produce over 1000CCA and therefore be able to start almost any engine type.
This is where the dual purpose really comes in to play, if you have a large Ah capacity battery and the manufacturer uses high quality active material, pure lead, plastics, resins not only will it last many years it will have high cranking output and therefore be a sprinter and a marathon runner all in one.
