More Battery Confusion

I'm still struggling with this battery issue. I did some more research, and the few sources I could find that discussed deep cycle battery usage, indicated that I should get about 70 - 80 amp hours from my current battery.

In a previous post, I stated that I only used 12 amp hours. I was wrong.

I did some more math - which is much more advanced than any writer wants it to be.
Hopefully, I got this right by using the formula for AC single phase watts to amps calculation formula (it's o.k. if your eyes just glazed over. Mine did, too, the first time I saw this formula).

Shop light doubling as a porch light would go something like this:
65 Watt Bulb / (0.8 x 110 V) = .73 amps
To get amp hours, I would simply multiply .73 by the number of hours the light was on.
Since it was just a few hours, I'd say a light did not drain my battery. The light set up's biggest offense was that is looked a little white trashy.

My next offender was the little fan that I put in a window for about 10 hours. I think it pulls about .8 amps. So that would get me up to 8 amp hours, and since I used a weed eater for a an hour or two, the weed eater must eat power like crazy.  Clearly, I need to investigate power tool power usage more.

This sucks.

Basically, I think I need one battery for the fan, and one battery for lights and other small electronics.
I also should probably buy a 100 watt solar panel to recharge the fan battery each day. That's another $150 to spend. Otherwise, my 8 amp battery charger, on the generator, will take about 2.5 days to fully charge an 80 amp hour battery. That's a lot of propane!

I read somewhere that deep cycle batteries slowly discharge even when they're not in use. I'm hoping my trickle charger slows that enough to keep any battery charged while we're away. (Also, thanks to Hank Finn for educating me on batteries a bit more. His recommendation is to charge it slowly because batteries like that better.)

Anyway. The moral to this blog post is this - off grid power is expensive.
Moral #2. Never underestimate the mathematical ability of a doomsday prepper. I love to make fun of these people, but dang. They must have pretty great math skills to live off the grid! I apologize to all you conspiracy theorists.

Math rules.