From a note I read here on battery testing, it seems like a long
-offset voltmeter would take just two wires, and give a fair idea
of the battery state.
You can arrange a long offset meter with a zener diode a series
resistor and a 'test' press-button with a suitable milliammeter.

For example: an 11 volt zener, a 1 milliamp full scale meter
and a series resistor of about 4000 ohms wired through a press-button
to ground, to give a scale reading from 11 to 15 volts.

You would need to make a custom scale - perhaps with a red line at
12.6 volts, and zeners being what they are, you would need to
calibrate the scale with a DVM one time.
[Edge-reading meters were often convenient to fit with a custom
scale]

Brian W

On 24 Jan 2004 20:36:31 -0800, (Parallax)
wrote:

Another poster got me thinking about an old idea of mine. My
batteries are hard to get to for testing (specific gravity) So......

Have a special battery cap made with a tiny specific gravity tester
built into each cell cap. It will also measure fluid level. The info
is sent by wire to a meter in the cabin that can look at each cell.

As far as gadgets go, this would be really useful. Does it exist?