You can't charge "A" size
batteries as singles in that charger because the current passed by the charger is more than the rated charging current capacity of the batteries. Hence the heat. Bottom line, if the battery fits, the Nitecore will charge it. I had the same question about this when I bought it, as I use a Provari Mini, but alas, it does charge 18350s. I can and do sometimes charge 350s as singles, no problem.
Happy
vaping!