Cycle in a Battery
A battery’s cycle is known as a discharge and a recharge cycle. So, you charge your battery up, and then discharge is by using it. That’s a cycle. A shallow cycle battery is meant to give relatively quick bursts of energy and not be used for a very long time before it’s returned to a fully charged state. A deep cycle battery is meant to provide extended usage of the battery going well below 50% discharge before it is recharged.
Understanding this simple theory, we can quickly relate this to different uses of a battery, which is very important to think about before you select the type of battery that you’re going to buy for your specific system.
Let me provide two examples.
Shallow Cycle Battery Example
The first is a car battery. This is a battery that doesn’t run all day long, it’s a short burst of electricity that is requires the turn the ignition and to give the car a big boost to start. Once your car is running, the usage of your car battery goes down to nearly zero… kind of.
Can you think of any other types of shallow cycle examples? Perhaps a spark for your bbq? How about a toaster oven?
It is very important to note that Shallow Cycle batteries do not like to be discharged over long periods of time. If you want to be nice to your shallow cycle battery (ie. extend the life of it), you’ll want to have a discharge control circuit that will cut off usage of the battery after it has been depleted by about 50%, and recharged as soon as possible. You can see from the graph below, that the less you discharge your shallow cycle battery (Depth of Discharge – DOD – is less), the more cycles you’ll get from your battery.
Depth of Discharge lifetime for a shallow cycle battery graph from pveducation.org
Deep Cycle Battery Example
The second is your smartphone. This is a battery that runs all day long, every day (if you use your smartphone like I do!). There is no big burst of energy required to start an engine or fire a rocket off, it’s just a continual drain (depending on how many apps you have running).
Contrary to the shallow cycle battery, the deep cycle batteries can go beyond 50% discharge all the way up to 80% discharge before its usage should be cut off by the control circuit and recharged.
From the graph above, you can see that if you discharge your shallow cycle battery to 50% and recharge it from there, you’ll most likely get around 500 cycles from your battery. However, a deep-cycle lead acid battery should be able to maintain a cycle life of more than 1,000 even at DOD over 50%.
Charging Also Effects the Cycle of a Battery
If it’s not already clear, to maintain the health of your deep cycle or shallow cycle battery, it’s very important to have a smart charge/discharge monitor. Not having one will result in either overcharging or undercharging with most definitely results in drastic loss of capacity from your battery, as shown by the graph below.
Battery Capacity defined by Charging cycle from pveducation.org
Other Factors to think about in Battery Usage
So now it should be abundantly clear that charge and discharge rate of a battery is very important to know before picking out your battery for your system you’re designing.
What else effects the life cycle of a battery?
Temperature is a very big factor. The colder your battery is, the less capacity it has to deliver to you. As your battery gets colder it will be as if it can no longer maintain full capacity in spite charging it for very long periods of time, and maintaining the same usage it will be depleted much quicker. However, this doesn’t mean you should cook all your batteries! The higher the temperature of the battery, the quicker it ages, so the number of cycles you get out of your battery will rapidly diminish.