Having seen this product on the interwebs, I knew I had to have one. $26.31 USD shipped to my door in NC.
 
SparkBright Voltage Monitor
 
Features:
 
- dims automatically in response to ambient light
 
- fully waterproof & shockproof (IP rating pending)
 
- available in three LED sizes; 10mm, 8mm, and 5mm
 
- indicates your battery’s charge condition and confirms alternator operation (if applicable)
 
- available in 6v, 12v, or 24v versions (or other voltage from 3v min. to 32v max.)
 
- extremely precise (12v unit is +/-0.03v)
 
- 600mm long flexible flying leads (longer leads available on request)
 
- reverse polarity and overload protected
 
- simple two wire connection to positive & negative
 
- very low power consumption (8ma in bright light, 1ma in darkness)
 
- suitable for direct connection to battery (simply cover to reduce drain when garaged)
 
It's quite an intelligent little device that even autodims based on ambient light. This is how mine looks. It's the 5mm model and snaps right into the hole next to the 12v outlet. Just needed to drill it out another 1mm. I soldered it to the 12v socket wires on the backside which is a switched circuit. No parasitic draw.
 


 

Nice. I forwarded to a non-FJ friend. He's always consuming batteries.

That does look handy and clean.

I have an older, simular setup on my ST1100, saved my bacon when the alternator died!

I installed a combo LED digital volt meter / 2.1 amp x 2 USB power port...