What are Shallow cycle and Deep cycle Batteries?

What are Shallow cycle and Deep cycle Batteries?

 A shallow cycle means discharging only a little, say 20% or less, and recharging back to full. Such batteries are used in the automobiles and are designed with rather thin plates which give a large surface area to provide a lot of current for a short period, as needed while starting the vehicle. At the start such a battery delivers several hundred amperes for a few seconds, then the alternator takes over and the battery is quickly recharged. These types of batteries are not suitable for solar PV system and would not last very long. PV systems demand continuous and deep discharging and recharging of batteries. Therefore, deep cycle batteries are needed for the PV systems; they deliver fewer amperes but for longer hours between charging. Deep cycle batteries are designed with thicker electrode plates and thus, have less overall surface area. They are suitable for giving current for much longer periods. They can normally withstand up to 80% discharge (better not to use the remaining 20%). However, it is recommended to use only 50% as the normal maximum discharge and leave 30% for emergencies.