These are bigger than one inch but might fit your need.
http://www.hangtimes.com/chargers.html
Aviation Concepts On-Board Voltage Monitor, just $42.95
Designed specifically for use mounted on board your aircraft. Dash mount or install in the fuselage side near your switch port. Use for either Rx system or Ignition system voltage display.
Works with any Li-Poly, Li-Ion system as well as with regulated and non-regulated 4.8 and 6.0v Nicad and NiMH systems. The meter comes pre-wired and is compatible with any Futaba J, JR, Hitec or AirtZ system. Plug it into any unused port on the receiver or it can be Y harnessed with any servo or the battery lead. Mounts in a 1 5/16" x 13/16" opening.
OR, Aviation Concepts On-Board Digital ESV w/Load, just $49.95, same size as unloaded version.