Up for sale is a new DC-to-DC Step-Down Voltage Converter.

Manufacturers vary.

Can be used for a wide range of applications. It is fully sealed in a plastic housing.
It also has built-in over voltage, under voltage, overload, overheat and short circuit protection.
I still strongly recommend implementing circuit protection by using a fuse or circuit breaker.

Input Voltage: 12 Volts DC
Output Voltage: 5 Volts DC
Output Power: max. 3 Amps (15 Watts)
Efficiency: > 90%

Operating Temp: 10°F - 160°F (-10°C - 70°C)

Dimensions (w/out mounting tabs): 1-7/8" x 1-1/8" x 5/8" (48mm x 28.6mm x 16mm)
Mounting holes: 1/8" x 2-1/4" (3.2mm x 57mm)
Wire lengths: approx. 5" (125mm)

Please see photos.
Questions welcome. Thanks for looking.