VIDEO – What is a battery cycle?

In this film we explain what is meant by a “battery cycle”, also often referred to as a “charge cycle”.


In this video we’ll be explaining what State of Charge means, how it describes a battery cycle, what cycle depth is and what we mean by deep cycling, cycle length and cycle life.

State of charge is a measurement between 0% and 100% of how much charge a battery is holding at any moment in time. 100% State of Charge means a battery is fully charged, 0% means completely discharged.

Lets consider how that can be seen in a battery that starts a car.

The battery turns the engine so its discharging. As soon as the engine starts the battery begins recharging.

If we plotted this on a State of Charge graph it would look something like this.

This discharging and recharging process is known as One Cycle.

OK – Time for a quick reality check. The graphs we’re using in this video are for illustration purposes. In the example you’ve just seen the discharge took seconds but the recharging would actually take several minutes.

So thats a battery cycle, what is cycle depth?

The battery that started the petrol engine didn’t discharge for long but what about a heavier diesel engine?

The battery here has more work to do heating up parts of the engine before turning it over

So its discharging as it heats the engine and then discharging more as it turns the engine.

If we compare the diesel battery State of Charge graph with the one for the gasoline engine the difference is clear. The battery powering the diesel engine goes to a lower state of charge, it is a deeper cycle.

But this isn’t always what is meant by deep cycling which is a specific term for batteries that are designed to go to a very low state of charge.

Consider applications such as parked up motor homes and caravans, your laptop or cell phone or complex computer systems. These batteries are designed to discharge over long periods to low states of charge.

Compared to the gasoline or diesel engine starter batteries they go through much,much deeper cycles.

Different types of batteries are better at different types of cycling. You can learn more about these differences by visiting the BatteryGuy knowledge center at and searching ‘Deep Cycle’

Now lets cover Cycle length. Its probably clear to you that one cycle of a gasoline engines battery takes much less time than one cycle of a smart phone or laptop battery.

If we update our graph to reflect this we can see visually the difference in cycle length between a battery that starts a gasoline engine, one that starts a diesel engine and one that powers a laptop computer.

Again different types of batteries are better at handling different cycle lengths. For more detail on this visit the BatteryGuy Knowledge Base at and search ‘Cycle Length’

Finally lets explain Cycle life. All batteries, after a certain number of cycles, will stop working – this can happen suddenly or they can just slowly gett worse at taking charge. Some types of batteries can only cycle a few hundred times, others can cycle thousands of times.

In certain cases a battery that dies after a small number of deep cycles will last much longer if the cycles are shallower. So cycle depth can have an effect on cycle life for some battery types.

To find out more about this concept visit the BatteryGuy Knowledge base at and search ‘Cycle Life’

In this video we’ve covered what state of charge means, how it helps describe a battery cycle, what cycle depth is and what we mean by deep cycling, cycle length and cycle life.

Remember to subscribe and check out our other videos especially ‘What makes a deep cycle battery different’ and if you want to read more simply search BatteryGuy Knowledge base.

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