Full power 12 volt to 48 volt dc dc converter 15A 720W boost step up transformer - AliExpress
48 volt to 12 volt DC/DC converter, 40 to 65 volt input, 200 watt, Heavy Duty, military marine and industrial grade, 12V, 13.8V output.
CUI 20W DC-DC Converter 48V (18-75V) to 12V 1.6A
Fully Isolated 48V to 12V DC/DC voltage converter 300 Watts peak, PVTC315-48 -12
DC-DC Boost Converter, 12V to 48V | ATO.com
Amazon.com: XWST DC 12V Step up to 48V 2.1A 100W Converter Voltage Converter, 48Volt Regulator Waterproof DC/DC Boost Transformer Power Supply (12V to 48V 2.1A) : Electronics