I am in the process of charging some nimh cells similar to the 18650 liIon. These are 4000 mAh cells and fit nicely in the 19650 holders. I set the charger to nimh and 2A charge rate, automatic, and cur limit. It charged a cell for about 15mins and then started beeping while displaying on the left of the LCD, done TRK. What does TRK mean and why is the charger still trying to charge the battery?