if you buy two 6V golf car batteries from Sam's or Wal-Mart-fall-apart, those are 220 amp hour batteries. When you series two 6V batteries to get 12Volts, it will still be 220 amp hours, but at 12 volts. Series wiring adds voltage. Parallel wiring adds current (amps).
The next thing you will have to decide is what type(s) of charging sources you will have. And these charging sources, whatever they are must, with no exception, exceed your load watts by at lease 20% or you will kill those batteries in short order.
Example: If you determine that your system averages 100 watt hours of drain per day, you will need a minimum of 120 watt hours of input per day.
At 12 volts, 100 watts is 8.33 amps. By the same token, this works out to about 8.33 amp hours.
Let's say your source is solar, a 10 watt panel at nominal 12 volts:
The sun shines an average of 5 hours per day (it won't).
The solar panels put out 10 watts (this is their peak rating (they won't)).
This equates to 50 watt hours per day of input. That is half what you used. In the end, ruined batteries.
Double the solar panels, and even though it will take longer, ruined batteries.
Triple the solar panels, and it will be close.
Three 10 watt panels, which make 50 watts each for 150 watts total. You needed 120W input so now you are slightly ahead of the game. Still a chance for ruined batteries unless you are very careful.
Remember that solar panels are rated at their peak watts and at an optimal voltage (not necessarily the voltage of your system) and in direct sunlight. For most installations, the output is generally less sue to directional inaccuracy, voltage differences and other factors.
Now, add wind to the mix and the numbers go crazy again. Same basic issues apply. How much will it make per day on average. Subtract a minimum of 20%. This is what you have to work with as far as output.
As others have said, read, read, read. Otherpower.com and other sources are wonderful for explaining all this stuff.
Doug
