Help convert this charging indicator circuit
The circuit appears to trigger when it sees current flowing into the battery, with the 1M resistor only being there to create an offset to keep it switched off at 0 current, (op amp input offset voltage)

To make this circuit work on a higher voltage you should only need to increase the LED resistor value, to about 4.7K, and reduce it back if the brightness is too low for you. 

The op amp is rated to run up to 36V, so your still in its specs

edit: R3 can likely be reduced in value and still work.