I received a replacement for the failed fan in my 24hr FARS.
It is a 7758, not B.
Since it is 6 months old, if the same part I'll open the box and install it. I wouldn't need to replace batteries.
If they're different, no need to open it and the ISS.
I'm guessing they are the same fan assembly, but don't want to disassemble the ISS to find out.