The workings of a battery charger?

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?

Usually it's something like constant current until a certain voltage is reached, then constant voltage until the current falls below a specified value.

Did you read the datasheet? They usually describe it's charging behavior.

jmusther:
So I’ve become curious as to how battery charging works. I had assumed that the IC was providing a constant

Depends upon the battery chemistry.

Different batteries need different charging regimes.
Charging chips can be designed for diffeent batteries or multiple battery types rarelly

The general type of battery charger will consist of two output terminals marked red and black. It should also consist of an ammeter to display the charging current and a voltage selector switch. Begin by selecting the appropriate charging voltage as per the battery used.