Charging batteries with solar panel
The chip tries to charge the batteries, but it can't know if there is only battery or load too, so it is unlikely that the charger chip can determine when the batteries are full.

The charging chip does not output anything, it just charges batteries. The output is the battery output. You can't use a resistor to drop voltage, you need a buck converter.

You can freely set the total expected battery voltage with resistors. So you can connect two batteries in series if you want 7.4V output. Or two batteries in parallel, which just looks like one larger 3.7V battery.