Volks:

Let me add a bit to this battery thread.  Although I'm not
one to quibble with Mr. Davidson and the prodigious research
he performs, and my thoughts may be no more than a mirror
image of his ideas, it is my understanding that a deep-
cycle battery is designed to provide SUSTAINED , uniform
electrical output over a relatively longer period of time.
An automobile battery is designed for a relatively high
"burst" output of electrical energy (and then be rapidly
recharged by the alternator).  Both batteries can be drawn
down relatively frequently, but the auto battery prefers to
be immediately recharged.

Another thought is that deep-cycle batteries do have, in
general, a limited number of "cycles" they will provide.
The "deeper" a deep-cycle battery is discharged (below 50%
discharge, in general) in each cycle, the shorter the
overall battery life.

In determining power usage of equipment (load in amps) be
certain that all power loads have been converted to the same
units. (A laptop computer rated: 1amp@ 110V would be drawing
approximately 10x's that from 12V battery) Power (watts) =
applied voltage x circuit current in amperes (amps).

Okay, I'm done. (it's snowing here and I'm stuck inside)
Thanks again, Bill, for all your work detailing the wiring
issues for an additional battery.

- - George Chapman, 91 GL
    Lake Almanor, CA