The small DPDT 8-pin 1Amp relays I used in a project were rated for 60volt DC standoff (when they don't have to switch any current). I think lifetime is >100.000 switch times. Use a relay with datasheet.
A single n-channel fet needs a kickback diode between drain and 48volt (cathode to 48volt).
A full h-bridge can utilise the integrated diodes of the mosfets.
Leo..