CXA1512 LED CC/CV driver design?
First impression:

The below figure from datasheet says that, it has a forward voltage drop of about 20 V at room temperature, and will be more at lesser temperature.

LM43602 or TPS54231 can switch the output to about 21 V from a  input of 23 to 25 V. I would use 8 battery cells (total voltage of ~29 V to ~23 V)



STCS1 or similar rated constant current LED driver (1.5 A max) if the power section is only for driving LED section.