The portable work I've been doing on Georges Island has been great practice for this kind of operation. This last weekend Sandy and I went out there with just small (17Ah) batteries and a solar panel, a very similar setup to what I hope to use on Montserrat.
One of the questions I had out there was "how much battery have I eaten so far?" I was periodically checking the battery voltage with the small voltmeter I had brought with me (it now lives with the Icom 7000 stuff permanently) but what I really wanted to know was the number of amp-hours I had sucked out of the battery and how much of the battery might be left. Also, you can damage batteries if you run them down too far, so I would like to know when I might be approaching that point. I need data!
Luckily, there is a gizmo that gives me exactly what I need. It is distributed by West Mountain Radio and it is called the Super Whatt Meter. The unit comes with PowerPoles so it goes easily with all the other power connections I have. The unit draws only a few milliamps to power its little processor and run the display. It computes all sorts of stuff but the big things I was looking for are voltage, amps, and the total number of amp-hours drawn thus far. This is exactly the information I need to assess the health, efficacy, and projected life span of my battery during a portable operation. I've got a picture of tonight's test setup (sorry, it is a little dark).
The display shows the 7000 drawing 1.32 amps, 16 watts, with the battery voltage at 12.62 volts, and 0.780 amp hours have been drawn from the battery. Pretty nice! The display alternates between amp hours and watt hours, too. Putting things in perspective, my "15 watt" solar panel (which probably puts out about 10 watts when not in the optimum conditions the specifications call for) supplies insufficient power to run the radio on receive. Compare the 7000 to the Elecraft K2 that draws about 35 mA on receive!
The Super Whatt Meter retails for $69.95. If you want to put your own PowerPoles on it you can buy the Astro Flight unit for somewhat less. (Just Googling around I found one online here). If you plan to do any portable operation with batteries, this can be a great source of data. It seems like a nicely thought out device. I've just made mine a permanent part of the 7000 kit.