Are my rechargeable batteries already worn out? How to assess the condition, state, and age of the rechargeable batteries I own?

1. Assessment of the battery's age

Every reputable manufacturer MUST place the production date on their batteries – it may be encrypted (in code), but a reliable seller/manufacturer should be able to determine when a given battery was produced.

Why is the age of the battery so important? 

A cell that is 2 years old (or more) will usually be more unreliable than brand new cells – even if it has not been regularly used or heavily exploited. 

It is worth knowing that international manufacturing standards used to assess the quality of Ni-MH batteries no longer even specify the criteria that a cell must meet after 2 years from the production date – such a cell may still be quite useful, but in the case of the most stressed cells with high capacities, degradation is noticeable after such a period. 

2. Measurement of the usable capacity of the battery (from discharge)

There are many chargers on the market that, according to manufacturers' assurances, can measure the capacity of batteries. Unfortunately, there are far fewer chargers that do this reliably or accurately enough.

If we have a suitable charger from brands like everActive, Xtar, or Eneloop, this is a relatively easy element to verify. 

The capacity result obtained on a given battery must again be related to its age or the time that has passed since its purchase. If the battery is new, freshly purchased, it should show a capacity close to its nominal capacity; if after several cycles/discharges its capacity is still more than 5% lower than what the manufacturer declares – it is worth taking a closer look at it. 

[Remember that to assess the capacity of the battery, we must perform a full charge and discharge cycle of the battery. The value obtained after a full discharge indicates the actual capacity of the battery.]

A battery does not have to and usually cannot maintain full usable capacity for many years. The same is true when our battery has been in use for a longer time. 

The usability criterion for Ni-MH cells is 60% of the nominal capacity, while for Li-ion cells it is 80%. A permanent drop in capacity below these values may be a reason for claiming the cells during their warranty period (typically 2 years). 

 3. Measurement of the internal resistance of the battery

In the case of Ni-MH cells, this is an element after which we will notice a drop in battery performance even faster. An increase in resistance values above 200-300 milliohms already indicates significant degradation of the cells, and such values should not appear in typical applications during the first months or even a year of use. 

We can measure resistance, just like capacity, in a suitable charger – e.g., everActive NC-3000 (for Ni-MH cells) or UC-4200 (for both Ni-MH and Li-ion). 

If we do not have a suitable charger, we should equip ourselves with a voltmeter (multimeter) and some simple load, preferably drawing about 300-1000 mA from our battery (a regular 4.7 Ohm / 5W resistor will work for both Ni-MH 1.2V and Li-ion 3.7V).  

For the measurement, we need a battery charged at least 50%. 

We measure the voltage on such a battery, without a connected load (resistor), then we connect our resistor between the + and - terminals and record the voltage reading directly on the battery after about 1-2 seconds. 

The second reading will be lower – the value of the voltage drop will be higher the higher the resistance of our battery – if under such conditions we record a drop higher than 0.1 V on a Ni-MH cell, and above 0.3 V on a Li-ion cell, it is worth claiming such a cell. 

4. Measurement of the cell voltage (?)

Unfortunately, measuring the voltage itself will not give us anything – especially in the case of Ni-MH cells – we cannot even accurately assess the charge level of such a battery based solely on the voltage value – we wrote about this in another post.

5. Checking the battery on a battery tester (?)

Usually, such a test is also useless – even on heavily used batteries, simple analog and digital testers show quite optimistic values. Additionally, before such a test, we must be sure that the battery has been properly charged.

Summary

In our practice, it often turns out that claimed cells easily meet the 2/3 criteria – achieving proper capacities, having low resistance, and yet not working for the customer. The most common reason is: improper charging of the batteries (low quality of the charger used), lack of attempts to repeat the charging process in the case of heavily dependent cells, as well as a trivial reason such as lack of proper contact between the battery and the contacts/springs in the device's basket. Less often, the problem lies in the device, which poorly tolerates operation with any batteries – although such devices still occur. 

Copying the content of the article or any part of it without the consent of a representative of Baltrade sp. z o.o. is prohibited.