> Or follow suit with the car audio crowd and install more batteries...

If you were to do that, to keep 35W at 12V alive for 7 days, you would need:

7 days / ( (50 A * 1 hr * 12V) / (35 W) ) = 10 batteries (google the LHS)

You're likely only to find 50Ah batteries.  Optima yellow-top deep-cycle
($200) is rated at 55Ah - YJMV (Your Jouleage May Vary).  Each battery is
at least 60 pounds also.

What's the application?

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Dave Carlson <thecubic at thecubic.net>