How to correctly measure the capacity of an AA 1.2V or 18650 3.7V battery in chargers with capacity measurement?

What is the capacity of a battery expressed in mAh (milliamp hours)?<\/span><\/h2>\r\n

The capacity of a battery is the most common (which does not mean the best - but that's a topic for another article) parameter used to determine its performance. Based on this, we can assess how long our battery will operate when loaded/discharged with a specific current. Thus, a nominal battery with a capacity of 2000 mAh should be able to deliver 2000 mA of current for 1h or 1000 mA of current for 2h, 500 mA of current for 4h, etc.<\/span><\/p>\r\n

mA - milliamp hours, is a unit of current/intensity, while h - hours, is a unit of time. The combined unit mAh tells us how much current was delivered (or accepted) by a given battery in a certain time.<\/strong><\/p>\r\n

Here appears the first, very common mistake made by users, as the mAh values returned by the charger should not always be associated with the total capacity of the battery (performance) declared on the battery label.<\/span><\/p>\r\n

Namely, many relatively simple chargers measure the mAh capacity value only during the charging of the battery. The value measured during charging will never be a measure of the battery's performance and we cannot directly use it to estimate the total available capacity of the battery (the value declared by the manufacturer).<\/strong> According to the previous explanation, in order to measure the real, true capacity of the battery, we must discharge it - and in this case, we are talking about a process that is exactly the opposite.<\/span><\/p>\r\n

Every start of the charging process, regardless of the degree of charge of the battery in the charger with mAh measurement, will start counting the mAh value from zero - now depending on how deeply our battery was discharged, the mAh value after full charging may constitute only a small percentage relative to the total capacity of that battery. We interpret this value in a very simple way - the mAh result obtained during charging tells us only and exclusively how much current in what time was needed for the charger to consider such a battery full<\/strong>.<\/p>\r\n

This often has no relation to its performance - the capacity of the battery that we can count on during its use/discharge, and in the case of Ni-MH batteries, it is not even clear to assess to what extent the battery was charged before being installed in the charger, and it is difficult, for example, to assess the self-discharge rate of such a battery solely on this basis<\/strong>.<\/p>\r\n

Why?<\/strong> The reason is very simple - primarily, every automatic charger must to some extent (preferably a small one) overcharge the Ni-MH 1.2V battery to detect its full charge.  These “excess” mAh<\/strong> is a value of about 10% of the actual capacity of the battery (which is even about 250 mAh for a battery above 2500 mAh) „go to waste” and will not affect the actual capacity result obtained later from the discharge.<\/strong><\/p>\r\n

This overcharging, depending on the ambient temperature/the temperature of the cells themselves, and even the specific battery, will sometimes be greater, sometimes smaller. In other words, it is impossible to assess how much of the measured example of 500 mAh from charging<\/strong> will later be converted into real capacity, and how much constitutes a "loss" related to the charging algorithm of the Ni-MH battery.<\/p>\r\n

The result will usually be the lowest upon recharging batteries that were previously fully charged. <\/p>\r\n

In the case of a charger where the mAh measurement occurs only during charging, the only way to estimate the total capacity is to first completely discharge the battery. Then the mAh value obtained during charging will be possibly the highest and usually similar to the capacity/performance mAh value provided by the manufacturer of our battery (for Ni-MH batteries, on average about 10% higher). However, this will still not be a clear and certain piece of information.<\/span><\/p>\r\n

The proper method to check the capacity of a battery<\/span><\/h2>\r\n

The only way to actually measure the total capacity is to discharge the battery that was previously fully charged.<\/strong> In other words, we need the capacity from discharge, not the imprecise information about capacity from charging.<\/span><\/p>\r\n

When considering the purchase of a charger, it is worth keeping this fact in mind, as slightly more expensive models have the ability to discharge batteries and actually measure their capacity. Examples here are the everActive chargers of the NC-1000, NC-3000 series for AA and AAA 1.2V batteries, or the universal model UC-4000, which can handle both AA R6 1.2V batteries and lithium-ion 18650 3.7V batteries.<\/span><\/p>\r\n

Due to the fact that the charger must completely discharge the battery, this process is quite time-consuming (usually takes at least a few hours), however, the capacity value that we will see at the end of such a test will be a good reference point and comparison to what the manufacturer declares.<\/span><\/p>\r\n

Beware of completely new batteries!<\/span><\/h2>\r\n

In the case of a completely new AA or AAA battery, the best result will only be obtained after it has been formed - usually after 3-5 full usage cycles. <\/span><\/strong><\/p>\r\n

At this point, it is worth pointing out another mistake that is made even by advanced users, and even in industry editorial offices where batteries and accumulators are tested. The fundamental rule is that the obtained capacity values are comparable to each other only when tested under exactly the same conditions.<\/strong> Values obtained using, for example, different models of chargers may and usually will differ. Above all, the market can find a lot of uncertain constructions that are characterized by a measurement error exceeding even 20%. Unfortunately, these erroneous charging/discharging algorithms in such chargers are nothing special.<\/span><\/p>\r\n

Having possibly the best, proven charger does not completely solve this problem - even the reliable and recommended chargers from the everActive brand differ slightly from each other in algorithms and testing conditions, capacity measurement, which is why the results obtained will never be 100% identical between different models.<\/p>\r\n

Every charger, regardless of its manufacturer, also usually has a slightly different charging algorithm, especially in the case of Ni-MH 1.2V batteries - a battery slightly undercharged during the test will always show a slightly lower capacity than one that has been slightly overcharged beforehand. So again, it is important to make any comparisons on the same equipment.<\/span><\/p>\r\n

Contrary to appearances, the quality variations in available chargers on the market are very large, so in the case of such functions as performance measurements, etc., I recommend using proven constructions - and such undoubtedly include eneloop, everActive, and Xtar chargers.<\/p>\r\n

If you have questions or doubts regarding measurements and results obtained on your chargers and batteries, let us know in the comments, we will gladly clarify any doubts.<\/span><\/p>\r\n

Author: Micha\u0142 Seredzi\u0144ski<\/span><\/p>\r\n

Copying the content of the article or its parts without the consent of a representative of Baltrade sp. z o.o. is prohibited.<\/p>","active":1,"text_mcedisabled":false,"image_alt":"","image_title":""},{"type":"text","image":"","text":"","active":0,"text_mcedisabled":false,"image_alt":"","image_title":""}],[{"type":"text","image":"","text":"

Recommended battery chargers with capacity testing:<\/strong><\/p>\r\n

[banner=103\/] [banner=104\/]<\/p>\r\n

[banner=155\/] [banner=159\/]<\/p>\r\n

[banner=158\/] [banner=160\/]<\/p>\r\n

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Frequently Asked Questions, Mah, Tests, Tips, mAh capacity

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