I'm used to powerful front lights, i've never looked back from a Cree of some sort (ULM T6 or something is the norm) and my 12v one is the best. It's designed for a motorbike, though i'm not sure it'd be legal here...
Anyway, i have a 12v polymer battery for this, though it also runs on an 8.4v battery i have for a SolarStorm.

My old e-bike's 24v battery would often run out on me, so i didn't want to run my headlamp from it. But my new e-bike has ample reserve, and a headlamp setting on the LED display. So now i want to connect the headlamp to the system.

I put a circuit tester on the headlamp feed cable, and it's showing 53.2v. I'm thinking that of all my Cree lamp units, they can handle 3.7v to maybe 16v, so 53v is rather a lot!

I've had a little look and 48v lights are available, but they're not cheap. I wondered if there's anything i can put on the line to transform a 48v supply to a lower voltage, but i'm not finding anything.

What have other people done?

I'm sure there are dc-dc converters that would do that. I searched for 48v to 12v converter, found this DC DC Converter 48V 12V | eBay
Just look for something that has a wide input range