Thanks for all the input guys. I will have to do more research before I
build this thing now, you've convinced me of a fire hazard.<g>
I may stay away from lithium's and just use a 7-10 Ah gel-cell. I'll
find out how many little panels I can stack to keep a trickle with these
cheap solar panels. It may turn out to be cheaper just to buy some
bigger 5W panels instead of messing with dozens of small ones.
I'm a hobbyist. I've been cobbling together useless crap for half a
century.
I was mostly using stuff I had on hand. If you're gonna buy stuff,
you have more options.
Keep your objective in mind.
If cost has any bearing on the project, there is no cost effective
solar solution. And solar is not portable. You have to find
a location to mount it where it gets sun year round.
If it fell off the window shelf and your battery discharged, you're SOL.
Ditto if you mount it on the roof and the squirrels ate the wire.
Once you screw it to the wall, you lose any portability advantage.
And you'll get so little power in the aftermath of a hurricane,
that you won't miss the connection.
If you're after emergency power, do you really want a system
that has a battery and some wire and a fuse wrapped in duct tape
hooked to some socket wrapped in duct tape into which you plug
some adapter that gets a light working?
It's all about the packaging. I'd want something with a handle
that I could pick up with one hand, flashlight in the other.
I don't recommend this one, but it was easy to click the link:
http://www.harborfreight.com/12-volt-jump-start-and-power-supply-38391.html
I'd get one without the jumper cables but add a 120VAC inverter built-in.
Without the inverter, they can be had for not much more than the
cost of a new battery. And for light loads, you can get cheap
inverters that plug into a cigarette lighter socket; still meeting
the one-hand rule.
And you can charge 'em with something like this:
http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html
Really doesn't make any difference whether it's one watt or five watts.
Neither will be of any real use in an emergency, and either can keep
the battery topped off.
Cobbling together a bunch of solar cells removed from other stuff is
ill-advised
unless you already have the other stuff.
The problem is not the circuit. The problem is getting them soldered
together without breaking 'em. And making sure the flux doesn't
corrode. And sealing them against weather using something that doesn't
block the sun today or turn yellow and block the sun next year.
And keeping the water out so they don't corrode and break the
connection. And finding a way to limit the voltage and current.
You want to be able to have some charge in the winter without
cooking the batteries in summer.
A wall wart solves all those problems. And many more not mentioned.
Designing an electrical system like this is trivial. The devil is
in the details: short circuit protection, connectors, charger, mechanical
details of the package...the one-hand rule.
FWIW, if you believe the graphs published on the battery sites,
you can get 4-ish amp hours out of a 7AH battery at a one-hour rate.
Your car battery can supply this amount of energy without breaking a
sweat...and a LOT more in short bursts. The system weighs a ton, but
it's on wheels ;-)
Looking back on all my hair-brained projects over the years, I wish
I had simplified my objectives, bought instead of built stuff
and spent more quality time with the (ex)wife.