looking for a reliable voltmeter to test NMH receiver battery
that I can plug into switch/charge jack located in the fuse

Radio South Pro-ESV Tester

What ever you get make sure you load the battery
I use one from hangar 9. I can select 1/2 amp or 1 amp load. How accurate it never gets calibrated. Close enough for government work

My favorite loaded battery tester is the Expert V-300. Horizon no longer carries them, but they are usually available new on Ebaay for less than $20. It loads the battery at 300mA and will test both 4 or 5 cell rx packs. It is the most valuable field tool I own. I check the rx batteries before each and every flight. It has saved me at least one plane that dropped a cell between flights.

Hanger9 Variable load meter.

The Hanger 9 meter with a 2A load would be great for larger models with digital servos.

It's good for checking any size airplane batteries.