Why Depth of Discharge (DoD) Matters in Solar Battery Storage System

13 June, 2025.

In simple terms the depth a battery is discharged is the percentage a battery has been emptied to its total capacity. The DoD is usually referred to in a percent, so a battery that has had a DoD of 100% means it has discharged to its full capacity. For example, if a 15-kWh battery was fully charged and had a DoD of 100% it has discharged 15kW. If it had a DoD of 80% it would have only discharged 12kW.

Batteries these days have a lifespan between 10-15 years however this can be heavily affected by the number of discharge cycles it has been through and the depth of those discharges. For example, a discharge of 10% will make less of an impact or degradation to a battery’s lifespan, than a discharge of 40%.

When researching into different batteries the manufacturers will usually specify a maximum DoD for best performance. For example, if it’s specified that a 10-kWh battery recommends a maximum DoD of 70%, you shouldn’t use more than 7-kWh from the battery without allowing it to recharge.

How does the depth of discharge affect battery life?

DoD has a great impact on the battery's life. A higher value of the depth of discharge means a large percentage of electricity is used before recharging. Generally, this practice leads to a shorter lifespan of a battery. The batteries that are frequently discharged deeply degrade faster than usual. Plus, they lose their capacity with time.

Let's go through some potential points about the depth of discharge and the battery's life. When you deeply discharge a battery, it puts added stress on its internal components. As a result, the plates may be damaged, and the capacity may be reduced.

Similarly, DoD is directly related to the number of a battery's charge-discharge cycles before it loses its capacity over time. Remember, different batteries come with different values of DoD, and we will discuss it in detail later in this article.

When a battery delivers a high amount of energy at a given time, its rate of discharge is higher. Some batteries are designed to do this, while others show this behaviour when they lose capacity. Continuing to discharge the batteries deeply may eventually lead to their short life.

Depth of discharge vs. Battery capacity

The battery's DoD and capacity are two different aspects of measuring its performance. When we talk about capacity, it means the total amount of energy a specific battery can store. It is similar to a tank's size, which shows how much fuel you can put into it. In contrast, the depth of discharge lets you know about the amount of energy that has already been used, as stated earlier.

DoD is a variable value that determines what percentage of capacity has been used. On the other hand, capacity is a fixed value that represents the total energy a battery can have. Let's understand this concept with an example.

Suppose the total capacity of a battery is 100 units, and 50 units are already consumed. It means the DoD will be 50%. In this case, DoD is half of the battery's total capacity. Understanding both the depth of discharge and capacity makes us familiar with the used and remaining energy level of a battery. In addition, it helps us know how long we can use a battery before connecting it with the charger.

If you want to achieve optimal battery performance, you should balance DoD and avoid discharging the battery deeply (still using some portion of its total capacity).

Lithium-ion vs. Lead-acid batteries

Lithium-ion batteries are a more recent technology compared to lead acid batteries. Though both come with unique features and a set of applications, Li-ion batteries are considered better than lead acid batteries in many aspects. Let's look at a few of them.

Li-ion batteries have a higher energy density than lead-acid batteries, which means they can store energy or electricity. When it comes to overall efficiency, lithium-ion batteries lead their lead-acid alternatives. Similarly, the lifespan of Li-ion batteries is longer than that of lead-acid ones.

Along with these parameters, lithium-ion batteries offer a better depth of discharge compared to lead-acid batteries. It means you can obtain more energy relative to the total capacity of a Li-ion battery than a lead-acid battery.

The DoD of lead-acid batteries is not more than 50%, which means you can't discharge more than half of their total capacity. On the other hand, at least 85% of the total capacity can be used for Li-ion batteries.

Suppose the total capacity of a lead-acid and a lithium-ion battery is 5kWh. Since the DoD of a lead-acid battery is 50%, it will only be able to deliver 2.5kWh of electricity, indicating half of the total capacity. If you want to buy reliable and premium quality lithium batteries, explore a decent collection at Sunselect.

Does a higher depth of discharge always mean better performance?

No, not at all. The better performance of a battery is not necessarily connected to a higher depth of discharge. For most batteries, it is advised to avoid high depth of discharge.

When we say a battery has a higher DoD, it means we can use more energy before recharging it. Though it may provide more electricity in the short term, it may negatively impact the battery's lifespan. At the same time, overall performance is equally compromised.

Frequent deep discharges are one of the batteries' biggest enemies, as they accelerate battery degradation. As a result, the battery's usable life is shortened, and its capacity is reduced.

If you want to make your battery last longer, remember to keep its depth of discharge within the limits recommended by the manufacturer, usually between 80% and 95% for Li-ion batteries. Following these limits not only extends the battery's life but also improves its health. In addition, it ensures that the battery can function properly for a long time.

How to calculate the depth of discharge?

It is super simple to calculate the battery depth of discharge. The steps you should follow while calculating DoD are as follows.

Step 1 :Determine the battery's initial capacity. This is usually presented in watt-hours (Wh) or amp-hours (Ah).

Step 2 :Now, estimate or measure the amount of energy that has been used from the battery's total capacity.

Step 3 :It is time to divide the amount of discharged energy by the battery's total capacity.

Step 4 :Multiply the answer with 100 to get the percentage value.

You can easily calculate the depth of discharge of your battery with the formula given below.

Depth of discharge = (used energy/initial capacity) x 100

Suppose a battery has a total capacity of 200Ah and 100Ah of energy has already been used out of the total. In that case, the depth of discharge will be 50% ((100Ah/200Ah) x100). As mentioned earlier, DoD is a variable value that can differ for each discharge cycle. Therefore, don't forget to calculate the DoD of your battery every time you use it.

The impact of temperature on battery DoD

All kinds of batteries usually perform well at room temperature. Extreme temperatures (low or high) have always been a trouble for most batteries. However, this is the area where lead-acid batteries outperform both lithium-ion and lithium iron phosphate batteries.

Batteries discharge faster in higher temperatures as the chemical reactions are accelerated. As a result, the lifespan is reduced. On the other hand, extremely low temperatures slow down the chemical reactions within the batteries, reducing their total capacity. Both extremely high and low temperatures increase the battery's depth of discharge.

If you want your battery to deliver electricity efficiently, keep it in the ideal temperature range. In addition, always follow proper charging practices and use active cooling systems to keep batteries away from extremely hot conditions.

How Do You Improve the Lifespan of a Solar Battery?

As a user, you can take several steps to increase the life of your solar batteries. Small things can make a significant difference in a variety of situations. Here are some suggestions to help you extend the life of your solar batteries.

Avoid Exposure to Extreme Weather

The temperature of the location where solar batteries are put makes a difference. Keeping the batteries at an ideal temperature will help to extend their lifespan. It will also help to increase its efficiency.

Under severe temperatures, solar batteries may stop working or malfunction. Solar battery capacity tends to diminish at extreme cold and high temperatures. These variations can both shorten and lengthen the battery's lifespan over time. During the winter, store the batteries at the appropriate room temperature.

Avoid Extreme State of Charge

Deficient and high charge levels might cause battery stress. Try an 80% partial charge rather than a full charge to reduce charging time. If you opt for a complete discharge, remove it as soon as it reaches 100%.

Charge Battery Properly

You get the most out of the battery, so charge it thoroughly. Pay attention to the charging time. Battery desulfation should not be used to extend the battery's life. Another crucial consideration is ventilation, which should always be noticed. Every gadget needs appropriate airflow to avoid overheating. Even when installing solar batteries, make sure the area is well-ventilated.

Conclusion

Understanding the Depth of Discharge (DoD) is crucial for anyone investing in a solar battery storage system. It directly influences the performance, efficiency, lifespan, and long-term return on investment of your solar energy setup. Batteries that are regularly discharged beyond their recommended DoD can suffer from faster degradation, reducing their overall capacity and potentially leading to costly replacements.

By choosing a battery with a suitable DoD rating for your energy needs and managing it properly, you can extend the life of your storage system, ensure more reliable power availability, and make the most out of your solar investment. Whether you're using lead-acid, lithium-ion, or another battery type, paying attention to DoD will help you balance energy usage with battery health.

Ultimately, optimizing your solar battery’s DoD isn't just about protecting equipment, it's about maximizing energy independence, sustainability, and savings for the long term.

Reach Out to SunSelect at 1300 867 353 for Expert Guidance and Money-Saving Options.
Explore the Reviews from Our Delighted Customers on ProductReview.com.au.