This is the VoltWatch2 on-board Receiver Battery Monitor for 4.8V and 6V NiCd and NiMH receiver packs.  This mounts on the outside of the airplane, so you can see at a glance the status of the receiver battery mounted inside.  These work great for airplanes and helicopters.

FEATURES:

• 7-LEDs provide instant, accurate battery voltage status of Low, Safe, or Max. Only one LED glows at a time
• Small switch to select 4.8V or 6V battery
• Very lightweight, only .15oz (4.3g)
• Unit can be mounted on the side of the fuselage, or under the plane's canopy.
• Draws amazingly low current - from 4-34mA depending on the battery condition
• Plugs into any open receiver channel
• One year warranty

INCLUDES:
One VoltWatch2 On-Board Receiver Battery Monitor
One 1.5x1" piece of double sided mounting tape

SPECS:
Length: 1.65" (42mm)
Width:  .63"  (16mm)
Height: .16"  (4mm)
Weight: 0.15oz (4.3 grams)
Current Draw: approx 4-34mA