Those sound like the batteries that are used for my Dob's fan (I bought the scope used, and the fan/batt setup is from AstroSystems). They are also available from RadioShack (used for cellular phones), but at a much higher cost!
Something that always worried me about them was the potential for them to vent gasses that would attack my mirror/coatings. So far, though, my coatings look fine. Anyone know what gasses are given off by lead acid or NiCad batteries during charging or use?
Lately, my batteries have gone south and I must replace them. I was thinking of just using the NiCads from my RC car instead. Since I am always forgetting to recharge the batteries, I thought it would be nice to have some batteries that I can quick-charge just before use (you can charge the nicads in 15 minutes).
Bob L