NMB Technologiess DC Axial Fan 24/48v 1.75a 42w Brushless 08038RA-24S-EA

You can series 2 of these fans for 48v applications.

2nd photo shows the specs of this fan. These are expensive elsewhere online. These were recovered from backup battery packs and are guaranteed to work like new. This is a legitimate fan, puts out a lot of air, and is trusted by very popular brand battery makers.

You'll be a big fan of this fan (pun intended).