Why Your AA NiMH Battery Be Detected As Li-ion While Charging

Nov 29, 2022 | XTAR

We noticed there were some feedbacks that the smart battery charger detected the AA Nimh battery as a Li-ion battery. Why this happened? In this article, we will share you the possible reasons and helpful tips.

There are usually two reasons for this issue. One is the charger may be broken, and the other is the battery is too old.

How to identify whether the charger is broken? You can try charging different batteries with this charger. If there are no problems with other batteries, the charger is good, otherwise the charger is damaged. In this case, you need to contact the battery charger store for repair. General top-brand battery charger manufacturers provide reliable warranty process.

Using an old battery is the biggest reason for the charger to misjudge Ni-MH as a Li-ion battery. This is related to the working process of the charger to detect the battery type.

How does the smart battery charger identify the battery type? It is mainly identified by the change of voltage.

When you put the battery into the battery compartment of the charger, the charger will charge the battery with a very small current, such as 200mA. Due to the different characteristics of the battery, Ni-MH batteries will not boost or only slightly boost the voltage under low current loading. But the storage range of lithium-ion batteries is between 2.5V and 4.2V, so the voltage boost is very fast. Then the charger uses a short time to identify again. If the battery voltage does not boost, it is judged to be a Ni-MH battery. If it boosts quickly, then it is a Li-ion battery.

An old battery has high internal resistance. So it goes from a low voltage to a noticeably high voltage very quickly when charging. And because the voltage rises too fast, it will be mistaken for a li-ion battery by the charger and start working based on a wrong assumption.

If you use an XTAR VC2S or VC4S, sometimes you may also find that the display on the charger screen goes back and forth between Ni-MH and Li-ion. It is the same reason.

How to judge the battery is too old? You can use a battery tester to measure the internal resistance of the battery. If the internal resistance is high, the battery is probably aging. For example, you may find that the internal resistance of your battery has reached 2000 mOhms. If you don’t have professional tools, you can put the old and new batteries of the same type into the charger to see if the charger judges the type of the new battery correctly. If the other batteries are judged correctly, there is probably a problem with this battery.

What will happen if the old Ni-MH battery is recognized as a lithium battery? Will it keep charging? Will the voltage go up?

If you are using an XTAR charger, since all XTAR chargers have a 0V activation function, the battery will be considered by the charger as a lithium ion battery to be activated. So it will be charged with the activation current of the lithium battery 200mA. When the Ni-MH battery is fully charged, the voltage will stop rising, but the battery will continue to heat up. Therefore, for safety reasons, it is not recommended to continue using such old batteries.

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