Anyway, I started researching gel-cell chargers just about the time this thread started up. I haven't seen anyone mention the Gleanings article in the July 1989 Sky & Telescope (page 97).
The article briefly reviews gel-cell characteristics and then presents plans for a charger you can build. I've been scrounging in my parts box and have most of what I need, so I expect I'll have something working in about a week (due to a severe lack of free time - the project looks like a 4 to 6 hour actual effort).
Since the article gave Radio Shack part numbers, I checked it out against my current Radio Shack catalog. A few parts are not currently offered, but they are easy to substitute. The most difficult issue for folks who do not have acces to other electronics parts sources is that Radio Shack no longer stocks the 18V transformer needed for the device, and the current catalog doesn't seem to have a suitable substitute.
Also, Radio Shack lists a 2.5 amp-hour, 6 V gel-cell in thier catalog for $11.99. Two of these in series would yield 12 V. The picture looks very similar to what a bought used, if two were ganged side-by-side.
I plan to use my gel-cell to drive my SPM mount and some home-made dew heaters. My SPM drive (an older model) came with a power pack that used eight D-cells which are expensive to replace and don't last all that long.
Clear skies or solder (I'm not a glass pusher)...Ken