How to identify a poor-quality energy storage system (or how Thunor was tried to be scammed) - Thunor Batteries, Inverters, Solar Panels

How to identify a poor-quality energy storage system (or how Thunor was tried to be scammed)


The autumn period is quite busy in the energy storage sector, as preparations are being made for winter storms and energy prices can fluctuate significantly during the winter period. We have also been pleasantly busy at Thunor and have been looking for additional battery element suppliers to meet demand. In connection with this, we encountered an interesting but time-consuming experience in October - namely, one battery element supplier tried to deliberately sell us counterfeit and poor-quality elements.

As we have already warned in our blog post, unfortunately, batteries are produced from lower-quality elements here and there. It is especially important to be skeptical of manufacturers and products for which the manufacturer or dealer cannot provide evidence of the battery elements in the energy storage systems.

Let's take a closer look at what buying a lower-quality battery means and what evidence of battery quality looks like.


High-quality vs low-quality cells

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

High-quality battery cells have a long lifespan and the storage can be used successfully for decades without major problems. The expected lifespan of Thunor energy storage systems is (with proper use) at least 20 years. High-quality energy storage systems retain their storage capacity or a large part of it over time, for example, the expected storage capacity of Thunor energy storage systems is also 60-80% of the original after 20 years.

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

Batteries containing lower-quality battery cells do not retain their storage capacity and can reach 80% of the capacity mentioned as an example in just five years. After 20 years, only less than half of the expected storage capacity remains, if they even work anymore.

It is also worth keeping in mind that defective battery elements increase the risk of fires and explosions.


Determining the quality (and class) of a battery cell

Each battery cell manufacturer performs measurements on its battery cells - the properties of the battery cell are measured, such as internal resistance, capacity, charging speed, stability, etc. In addition, battery elements are subjected to X-ray analysis, which allows for the identification of structural defects and thus the prediction of the battery cell lifespan. The highest quality battery cells have low internal resistance, high capacity, and very high stability.

The results of the tests are stored in a database and a QR code is laser-engraved on the battery cell, which allows you to verify the results of the report and the class of the battery cell.


The price of battery elements is determined according to the quality. A-class battery cells are significantly more expensive than B- and lower-class battery cells.

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


How Thunor Was Tried to Be Scammed

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 code on the elements.

We performed our usual quality control, and since several nuances raised suspicion, we decided to remove the black top coating from the element. As a result, it was clearly visible that the previous QR code had been ground off the battery cell and a new QR code had been engraved in place of the old code. Therefore, we were deliberately tried to be scammed and sold defective battery cells of unknown quality under the guise of A-class battery cells.


We contacted the supplier, who immediately admitted that they had accidentally sent the wrong elements and would send the correct ones in a few months. We of course did not agree with this, as we did not want to do any business with such a supplier.

In the end, the supplier partially compensated our costs and left the defective battery cells to us. We can use them to test some product development ideas and certify the box strength tests - something is better than nothing!


🚩🚩Red flags to help you identify poor quality batteries 🚩🚩

Here are some thoughts on what to ask an energy storage seller to check the quality of the batteries: 

  • What grade of battery cells are used in the energy storage being sold? Evading or not answering the question is a clear red flag. 🚩
  • Can the energy storage manufacturer or seller confirm the production history of the battery cells? Again, avoiding the question is a clear red flag. 🚩
  • Is the warranty on the energy storage five years or less? If you don't want to buy a new storage unit after five years, that is also a hint of poor quality. 🚩

Thunor provides you with all the battery cell information with the battery pack - you can study the battery cell test reports yourself if you wish.

On request, we will also provide reports on charging tests carried out in our factory, which show both the battery capacity and other parameters.

If you are interested, contact us at or call us at (+372) 55 941 611!


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