Do you want to monitor it or derive power from it, or both?
They are somewhat different problems - power supplies may hide moderate variations in input voltage, while just measuring voltage could be as simple as a divider made with high value resistors (possibly a few in series) and maybe a clamp as backup input protection.
I should have been more clear. The way I wrote it is confusing. I'm wanting to use a Omega2 /w AD converter to measure cells of the battery bank. The input to the AD will be done using a divider circuit.
My other problem is to power the Omega2 directly from that same battery bank as efficiently as possible. It's typically not recommended to use power from one of the 12V cells in the battery bank (unbalance), otherwise I could have used any cheap car adapter.