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What is DoD in Battery and Why is It Important?

what is dod in Battery

DoD in battery language is “Depth of Discharge.” It’s a widely misunderstood concept, more so when used to explain capacity vs. lifespan. Some batteries also allow a higher DoD than others. As you can see, the depth of discharge is an essential aspect of rechargeable energy devices. Learn more about it below.

What is DoD in Battery?

It indicates the extent of discharge or the amount of energy used out of a fully charged battery expressed as a percentage — and sometimes Ampere Hours(Ah).

A 60% DoD means 60 percent of the capacity is gone, and only 40% remains. The remaining power is then called the state of charge, SoC.

For example, let’s say you have a 100 Ah battery. When fully charged, its depth of discharge is 0%. Suppose you discharge it to 20% capacity. The depth of discharge will then be 80% (total used amount) or 80Ah.

What if you were to deplete it completely? Then, the DoD would rise to 100%, with a zero charge remaining. However, doing so could cause problems, which brings us to this critical question: why is battery DoD important?

Depth of discharge vs. total capacity and SoC
Depth of discharge vs. total capacity and SoC
Resource: https://www.researchgate.net

Why is DoD of Battery Important?

The depth of discharge provides essential information about usable vs. total capacity. It tells how much energy you can safely extract from a battery without affecting useful lifespan. To understand that better, let’s see how the DoD of a battery and its cycle life are related and if high or low is better.

DoD and Battery Lifespan

Batteries come rated to a certain number of recharge cycles at specific depths of discharge. Generally, a deep energy discharge reduces the number of these cycles. That, in turn, means reduced lifespan.

For example, a battery rated 2000 cycles at 30% DoD may only sustain 1600 cycles if drained to 85%. Generally, the less you drain your battery, the longer it will last.

It’s more like covering a distance by walking instead of running or drinking water in small sips instead of gulping it all down. Running would drain your energy faster, as gulping would deplete the water faster.

High and Low Battery DoD

A high depth of discharge means more power to use out of the battery’s total capacity. In other words, you can use your storage device for longer. However, as we have just seen, it has its downside.

In some batteries, it reduces the number of recharge cycles, shortening the lifespan. These batteries have lower depths of discharge, meaning you cannot safely subject them to deep depletion cycles.

Lithium types have high DoD values, over 80%, with some allowing complete depletion. As you can see, a high depth of discharge is better, but not all batteries can withstand it.

Depth of discharge is the opposite of the state of charge or SoC
Depth of discharge is the opposite of the state of charge or SoC
Resource: https://www.researchgate.net

How to Calculate the DoD of Battery

DoD is another name for discharged capacity expressed in ampere-hours or, more often, as a percentage. To calculate it, divide the expended capacity of a fully charged battery by its overall capacity and then multiply the result by 100.

For example, let’s say you have a 100Ah total capacity and use 40Ah. The DoD will be 40/100 multiplied by 100 = 40%. Here is another example:

Suppose you have another battery rated 120 Ah that you drain at 5A for 3 hours. The expended charge in Ah is the amount of current in amperes multiplied by time in hours or 5A x 3 Hr. = 15Ah.


The depth of discharge is 15Ah. To convert it into a percentage, divide the value by the total capacity, then multiply by 100, as shown here: 15Ah/120Ah × 100 = 12.5%. This capacity is well below the recommended level for most batteries and is safe.

Different batteries have varying depths of discharge
Different batteries have varying depths of discharge
Resource: https://youtu.be/CvB9t6onqcs?si=sVuIFHl9363SfqRU

What is the DoD of Different Types of Batteries?

Battery DoD varies depending on its type and other variables such as model, brand, or manufacturer. Let’s go through the depth of discharge of the most common types today: Lithium, Lead Acid, AGM, and Gel.

Lithium Batteries

The depth of discharge of lithium batteries is way higher, above 80%. The number of recharge cycles is also high, up to 8,000. The higher capacity and lifespan explain their widespread use in electric vehicles such as golf carts or the storage systems of RVs and other needs.

You can even drain some entirely without damage. However, it’s generally advisable not to extract too much power from any storage device as that could affect its cycle life in the long run, including the lithium types.

Lead Acid Batteries

The recommended discharge capacity is typically 50%. It means you can only use about half of the available power. On the other hand, the number of recharge cycles ranges from 300 to 500.

In addition to the low capacity, keeping lead acid batteries charged is recommended even when not used. Ensure you top them up with water, too, from time to time, so the plates remain covered at all times.

AGM Batteries

An AGM type has a DoD that ranges between 50% and 80%, making it a deeper-cycle device than the flooded or wet type. The number of cycles goes up to 500.

AGM stands for Absorbent Glass Mat, the glass fiber material separating the positive and negative plates. It absorbs the acid to make it a sealed energy storage device. These batteries are practically lead acid but with better performance characteristics.

Gel Batteries

This type has a higher number of cycles or, put another way, a longer lifespan. It has a recommended depth of discharge of 75%, making it better than the conventional lead-acid type in terms of the power you can safely use.

Like the AGM type, it’s a type of lead acid storage cell with a longer lifespan, withstanding up to 1000 cycles, which is only second to lithium batteries on our list.

Conclusion

Battery DoD gives you an idea of how much energy you can safely extract, which, in turn, can help prolong the battery’s lifespan. That’s because different batteries have varying levels of depth of discharge, with some getting damaged by deeper cycles than others.

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