Another great study on the performance of batteries and accumulators? - beware of the 7 deadly sins committed by testers. When is a test reliable/valuable? Check out our cheat sheet.

In my opinion, the above problem does not directly result from the „sponsoring” of tests or attempts to influence their results. In most cases, the blame lies with oversights and mistakes made by testers and reviewers.

We regularly point out repeated mistakes that can easily undermine the credibility of most tests found online.

1. Highly random testing conditions → lack of result repeatability

Comparable, repeatable testing conditions are probably the most important starting point for conducting any comparative research. Unfortunately, the most common mistake made by testers has its roots in these basics.

For example, a typical tester for AA/AAA LR6/LR03 alkaline batteries often has an advanced „machine” - a precise electronic load, where one can set the discharge current/power with great accuracy or simulate any load resistance. The batteries being tested are placed in a holder, the holder is connected to the load, and measurements are taken.

Here, an unobvious problem arises – typical battery holders are designed for very low loads. When applying loads of 300 mA and higher, the voltage drops on springs, contacts, and finally on thin measurement wires are so large (sometimes reaching tenths of a volt) that the percentage differences in the obtained runtime/ measured capacity can reach double-digit values. In such configurations, even obtaining the same results in subsequent repetitions of the test of the same battery is very difficult. With measurement errors of 10% or higher, comparing results loses any meaning.

The solution to this problem is to use a high-current holder and to bring four measurement wires (separate paths for measuring voltage and current), where the voltage measurement point is placed as close as possible to the terminals of the tested battery. How many times have you seen this done in such a configuration, with 4 measurement wires? Like me – probably rarely or maybe not at all.

In a typical popular test, even the best, most precise electronic load will not help if we do not ensure a certain voltage measurement directly from the battery. In a typical test scenario for AA/AAA cells, a cheap branded charger with a discharge and capacity measurement function will provide more repeatable testing conditions.

4. Lack of information about the age of the tested batteries and accumulators

Unfortunately, testers often lack basic knowledge about the products they are testing.

Even the highest quality specialist, an electronics expert who has the appropriate equipment to conduct tests, who knows how to ensure a possibly low measurement uncertainty, will not conduct the test correctly if they do not take care of products manufactured in a similar period.

According to standards, the permissible, permanent degradation of new, unused Ni-MH accumulators can reach even 30% after just 12 months from the original full charge. Of course, none of the branded accumulators ages that quickly, but particularly the highest-capacity accumulators clearly age over time regardless of how intensively they are used.

Similarly with alkaline batteries, where depending on storage conditions, they can lose from 3 to 10% of their capacity annually, and their voltage characteristics deteriorate (such cells achieve lower voltage and deliver less energy).

6. Testing procedure – or rather its absence

Browsing most tests, one can get the impression that the author believes they have the ideal equipment for testing batteries/accumulators and nothing stands in the way of conducting such a test.

The result of many such tests is, for example, the lack of any procedure regarding the forming of Ni-MH accumulators, or the use of inappropriate chargers, etc.

Ni-MH accumulators, depending on their age, capacity, and manufacturer, may require several cycles of full charging and discharging to be properly formed.

The target characteristics, voltage level during discharge develops gradually over time in Ni-MH accumulators – therefore, a minimum of several recharges seems necessary for it to have any comparative value.

For new accumulators (not stock), standards allow measurement during the first 5 cycles.

In some popular tests, accumulators are charged only once or twice. They are charged on equipment that says little about the correctness of the charging of the installed accumulators.

The process of properly charging Ni-MH accumulators is crucial for further tests, even in a typical usage test, where a given reviewer/tester has only one automatic charger. Unfortunately, we have a lot of uncertainty about whether all accumulators are treated equally and whether they have been properly charged. Especially when the process is not repeated several times.

In the absence of a sufficiently good charger, in the case of Ni-MH cells, a fair solution is „manual” charging of accumulators according to the standard PN/EN/IEC 61951:2, where a cell discharged to 1.0V is charged for 16 hours with a constant current equal to 10% of its capacity.

The process of testing, for example, alkaline LR6/LR03 batteries is at least theoretically simpler – although we usually see tests with loads of 300 mA-500 mA, additionally in questionable quality holders, which we mentioned in point 1. These are conditions under which such a battery has no chance of achieving its nominal capacities – the results will always be much lower here, sometimes unpredictable. Such a test will not provide clear information about the quality of a given battery. Unfortunately, tests with loads of, for example, 30-50 mA are much less common, which is a pity.

The process of testing Li-ion 3.6/3.7V accumulators should also start with a good charger that provides identical testing conditions for each accumulator, preferably one where the maximum charging voltage is in the range of 4.18-4.22V.

When discharging such accumulators, it is worth conducting tests with higher current values such as 3A/5A/10A, and even 20A in the case of high-current accumulators – here, it is even more important to have a very secure connection between the accumulator and the load and an uninterrupted voltage measurement as close as possible to the cell contacts.

7. Capacity measurement – the only correct measure of the performance of a battery or accumulator?

The vast majority of tests we encounter rely on synthetic capacity measurement. We will skip situations where the assumptions of such measurements are poorly chosen, or where capacity values are compared with charging (we discuss what proper capacity measurement involves in another post) – unfortunately, even where the entire test was conducted, it may seem correct, there is room for a large measurement error.

Examples include capacity measurements of batteries, accumulators on different equipment, and comparing them later one-to-one in the final summary.

Even under the same set measurement conditions, differences in capacity results can exceed 10-20% between different chargers/electronic loads. Even if all are characterized by the same high precision, they may differ in the way voltage is measured under load or the nature of the load (continuous/pulsed averaged over time). By using different measuring equipment, we can extract average mAh values from discharges and, for example, ensure that each of the accumulators is checked in each charger/load.

Ideally, if we add a practical test to such a synthetic test – for example, the number of flashes of a flash lamp or the operating time of a toy. Some testers have gone further – they tested previously frozen accumulators. However, such tests are very time-consuming, and unfortunately, it is currently difficult to find such projects.

If we do not want to waste time on tedious practical tests, there are other synthetic values that can be measured during capacity tests or their verification takes much less time.

Internal resistance – gives an answer about the current capabilities of a given cell – cells with lower resistance are much more reliable and promise longer use.

Energy mWh/Wh. Capacity does not tell us much about the actual amount of energy delivered by a given cell. We do not know at what output voltage it was achieved – and so a given battery or accumulator may have the same capacities, where one of the cells maintains about 10-20% higher voltage throughout the process. Such a cell with a higher output voltage will achieve exactly 10-20% higher results when measuring energy in mWh/Wh.

It would be ideal to check how the measured capacity/energy depends on the output voltage – this allows for accurate estimation of which cell will be better for even atypical applications.

What such results presentation might look like – check one of our tests regarding 9V cells.

Summary

Thank you for sticking with this lengthy post 😊

It still does not exhaust the topic of possible oversights, mistakes, and traps when testing batteries and accumulators.

Knowing these 7 most basic mistakes, one could venture a sort of ranking – „The worst battery and accumulator tests” – it is very possible that popular tests with a score of 6/7, or even 7/7, would be found there.

Unfortunately, it is very rare for a well-known editorial office, portal, or YouTuber to feel obliged to correct mistakes, or even to admit to them.

If we want to check/test batteries and accumulators ourselves, and do not want to spend a fortune on tests in accredited research laboratories, we should avoid the basic mistakes discussed above.

As a company with 33 years of experience in the market, specialized in batteries and accumulators, we are happy to provide substantive and product support in such endeavors – interested parties are encouraged to contact us.

If you have questions or doubts – ask below in the comments.

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