I've been setting up a system that uses a battery charger IC - Linear Technology's LT3652EMSE.
It works well, and I've been watching the voltage and current as a NiMH battery (6-cell) charges. I see the characteristic NiMH charge curve (voltage) and I see the charge current start at about 100 mA (what I programmed the IC for) and slowly fall until the IC cuts charging at 1/10 of the programmed current (so approx. 10 mA).
So I've become curious as to how battery charging works. I had assumed that the IC was providing a constant current supply to the battery, which explains the slow rise in voltage as the batter charges. But clearly the charging is not constant current, because I see that gradually fall, and I know many chargers terminate at C/10... so, I'm left slightly confused -clearly the charger is not constant current, nor constant voltage. So what's the story with battery charging?