How to Recognize a Poor-Quality Energy Storage System (or How Someone Tried to Deceive Thunor)

The autumn period is quite busy in the energy storage sector as preparations are made for winter storms, and energy prices can fluctuate significantly during the winter. We at Thunor have also experienced a pleasantly busy period and have been searching for additional suppliers of battery cells to meet the demand. In connection with this, we encountered an interesting yet time-consuming experience in October—namely, one battery cell seller attempted to sell us knowingly counterfeit and poor-quality cells.

As we have warned in our posts, unfortunately, batteries are sometimes produced from lower-quality components. It is particularly important to be skeptical of manufacturers and products for which neither the manufacturer nor the reseller can provide proof of the quality of the battery cells contained in the energy storage systems.

Let’s take a closer look at what purchasing a lower-quality battery means and what the evidence of battery quality looks like.

Quality vs. Poor-Quality Cells

An energy storage system is one of the most expensive components in the energy production or consumption management system, potentially accounting for 40-60% of the total investment cost, depending on the desired storage capacity. Due to the high cost of the storage system, it is crucial that the purchased storage system is of high quality and lasts a long time.

High-quality battery cells have a long lifespan and can be used successfully for decades without significant issues. The expected lifespan of Thunor’s energy storage systems is at least 20 years (with proper use). High-quality energy storage systems maintain their storage capacity over time, retaining 60-80% of the initial capacity after 20 years.

However, batteries assembled from defective battery cells may experience issues with charging speed and have a lifespan that is several times shorter. Therefore, Thunor uses only A-class, defect-free battery cells (Certified Automotive Grade) in the production of its batteries.

Batteries that contain lower-quality battery cells do not retain their storage capacity and may reach only 80% of their capacity within just five years. After 20 years, they are expected to retain less than half of the initial storage capacity, if they function at all.

It’s also worth keeping in mind that defective battery cells increase the risk of fires and explosions.

Determining Battery Cell Quality (and Class)

Every battery cell manufacturer conducts measurements on their cells—measuring properties such as internal resistance, capacity, charging speed, stability, and more. Among other tests, X-ray analysis is performed on the battery cells to identify structural defects and thus predict the battery cell's lifespan. The highest quality battery cells have low internal resistance, high capacity, and very high stability.

The test results are recorded in a database, and a QR code is laser-engraved onto the battery cell, allowing verification of the report results and the class of the battery cell. Below is an example of the QR code found on a battery cell.

According to Quality, Battery Cells Are Priced

A-class battery cells are significantly more expensive than B-class and lower-quality battery cells.

However, the market for lower-class battery cells is large, and they are often used to produce lower-quality energy storage systems, which are usually cheaper.

How Someone Tried to Deceive Thunor

As mentioned, we recently tested a new supplier and the quality of their products. The supplier sent us battery cells along with a database so that we could review the test reports based on the QR codes on the cells.

We conducted our usual quality control, and because several nuances raised suspicions, we decided to remove the black coating from the cell. As a result, it was clear that the previous QR code had been ground off the battery cell and a new QR code had been engraved in its place. Thus, an attempt was made to deliberately deceive us by selling defective battery cells of unknown quality as A-class battery cells.

We contacted the supplier, and he immediately admitted that he had accidentally sent the wrong cells and that he would send the correct ones in a few months. Of course, we were not willing to accept this, as we do not want to deal with such a supplier.

In the end, the supplier partially compensated us for the costs and left the defective battery cells with us. We can use them to test some product development ideas and certify box strength tests—so at least there’s some benefit!

🚩🚩 Red Flags: What to Look Out For 🚩🚩

Here are a few questions to ask an energy storage seller to check the quality of the batteries:

• What quality of battery cells are used in the energy storage system you are selling? Avoiding the question or not answering is a clear red flag. 🚩

• Can the manufacturer or seller of the energy storage system confirm the production history of the battery cells? Again, dodging the question is a clear warning sign. 🚩

• Is the warranty for the energy storage system five years or less? If you don’t want to buy a new storage unit in five years, this is also a hint at lower quality. 🚩

Thunor provides you with all the information about the battery cells with the power bank—you can review the test reports of the cells yourself if you wish.