Why the VC4S doesn’t show number IR when batteries are fully charged?

A customer told that he got some 18650 batteries fully charged on the VC4S, then tried on mode IR, but the charger didn't test the batteries' internal resistance, nor show the IR data on the screen. You may have the same question about the IR testing on VC4S charger before. Let's figure it out.

Our chargers adopt the direct current load method to test battery internal resistance. It means to apply a little bit larger current to the battery for a short period of time. Based on the voltage's change of the battery, also together with the applied current, it can calculate the DC internal resistance of the battery. If the battery gets fully charged, in case of over-charging, the charger won't test internal resistance in order to protect the battery. Besides, when the adapter input current is lower than 700mA via the charger, which is insufficient for internal resistance testing, the charger doesn't test IR either.

Any thoughts and opinions are welcome.

Thank you for that information. Describing the procedure your smart charger tests internal resistance makes sense why a fully charged battery will not work for an IR check.

Thanks for your kind supports! Hope this info can help some users。