Starting, Marine, and Deep-Cycle Batteries – A brief description
Starting - (often called SLI, for starting, lighting, ignition) batteries are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead “sponge”, similar in appearance to a very fine foam sponge.This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-120 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).
Deep - cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates at the cost of poor starting current given their amp hour (a/h) rating. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates – not sponge. This gives less surface area, thus less “instant” power like starting batteries need. Although these can be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge. Sometimes called “fork lift”, “traction” or “stationary” batteries, are used where power is needed over a longer period of time, and are designed to be “deep cycled”, or discharged down as low as 20% of full charge (80% DOD, or Depth of Discharge). Deep cycle batteries have much thicker plates than automotive batteries.
Marine batteries are usually a “hybrid”, and fall between the starting and deep-cycle batteries. In the hybrid, the plates may be composed of Lead sponge, but it is coarser and heavier than that used in starting batteries.