A battery in general can be considered as a power storage device. Depending on the power required, period of operation and some specific requirements, there are different kinds of batteries in the market. A commonly used battery, called lead-acid battery (normal), is mostly used in places where large amount of current is required for lesser periods. For purposes where consistent current flows are required for comparatively larger periods, a deep-cycle battery is used. Mostly these batteries can be seen in alternative energy projects such as solar or in our case backup solar systems.
Like every other battery, deep-cycle battery also works based on electrochemical principles where electricity is generated by chemical reactions in the cell. Batteries are designed as storage devises and not electricity generating devices. Generally, the current stored in the battery gets discharged over time due to internal resistance due to which every battery comes with efficiency factor. Deep-cycle batteries are designed to be discharged deeper over and over. These batteries, though they use same chemistry as any other battery, use thicker plates and such little design modifications to accomplish this task.
The deep-cycle batteries are designed to discharge as much as up to 80% time and again, which is accomplished by the thicker plates. More importantly the plates are not sponge but solid lead. This helps to reduce the surface area which is the reason for its less instant power unlike lead acid batteries. As such deep-cycle batteries are not used as car batteries, where a surge of current is needed for start-up purposes. Though it can be achieved if a suitable adaptation is employed. Like for example if a deep-cycle battery is to be used for starter purposes, the battery needs to oversized up to 20% when compared to traditional car batteries. It is not that deep-cycle battery cannot be used as starter but if same size as normal battery is used, it cannot provide the necessary cracking amps as a normal starter battery.
Deep cycle batteries are also used in industrial purposes as in forklifts and hence are also called traction batteries. Their use in forklifts is widespread as deep-cycle battery can be designed to discharge to as less as 20% of the whole capacity. This is also called 80% DOD (Depth of Discharge). When battery failures are considered, a mechanism called ‘positive grid corrosion’ stands among the top three reasons. This chemical mechanism is the main reason for the use of thicker plates in deep-cycle batteries. Over time the positive plate gets eaten up and falls to the bottom of the battery as sediment. Hence there would be no positive charge left to complete the circuit. Hence using a thicker plate for the positive charge helps in longer life of the battery. Generally there is a separation between the positive and negative charges, filled by glass or paper, as the negative charge tends to expand during discharge.
The thickness of the plates varies between batteries depending on the place they are employed in. For example, a car battery is 0.04” thick at plate while that of a forklift uses a plate of .26”(approx) thick. Most of the deep-cycle batteries does not use lead-calcium plates but use lead-antimony plates. This is because antimony increases the plate life and strength. The backdrop of using antimony plates is that the increase water-loss and gassing. Due to this the discharge rate can be very high, as high as 1% per day for older batteries! Though, the use of new AGM reduces the discharge rate to 1-2% per month as opposed to the old one, which may be 2% per week.
One of the main considerations while manufacturing a battery is that the acid must be separated and the separation should be made by installing walls. These walls, In addition, must be filled with explosive material. This increases safety as well as durability of the deep-cycle battery. Hence, deep-cell batteries, if produced by a reputable manufacturer, could be of great use considering the durability and high DOD along with the said advantage of consistent current capacity for longer periods.