Ian,
Any of the offerings mentioned are really not suitable for your application.
They are mainly used for a one at a time
"jump start" not a night long drain.
I recommend that you use
"Deep Cycle Batteries" They have a thicker plate than the other types and are suited to the type of power requirements needed by astronomers.
They do cost more, but the trade off is a constant and longer lasting battery.
At M.A.S we have a number of members using this setup, and they swear by it's reliability.
