"west" wrote in message
...
I know this question has probably been beaten to death, nevertheless I
hope
you will still indulge me.

During a power outage, which occurs frequently in Florida, I would like to
use a battery to power some communication gear. Although the battery is
12v
and not 13.8v, I think that the gear will still work OK (hopefully).

Question 1. I believe that car batteries have a low internal resistance
because their primary function is to provide a lot of current for a short
time. There are other 12v large battery types that will last as long as a
typical car battery. They are designed not to provide peak current, but to
supply steady state current for a long time.
For the life of me, I can't remember the name of those type batteries so I
can't do a google to find a supplier. I hope this is making some sense.


You are correct in noting that car batteries are, as a rule, designed to
deliver high current; long life is a secondary consideration. The way that
this is done is by using thin plates close together which gives lots of
surface area and hence lots of current. Such batteries do not tolerate
discharges well, it lessens their life considerably as the thin plates can
develop "holes" over time as they are depleted. Deep cycle batteries are
designed to supply less current for a longer duration and tolerate discharge
to 50-70% or so fairly well. They have thicker plates. Typical uses are
RV's and boats, which use lights, TV's, instruments, etc. without the engine
running quite a lot. I have been talking of lead-acid batteries here.
Another type is gel-cells. Gel cells contain the electrolytic solution
suspended in a "gel" which allows them to be fully discharged without
shorting out the plates and ruining the batteries... the gel holds the lead
ions from precipitating out of solution as the battery is discharged. Gel
cells must be charged at a slower rate, and cannot deliver as much current
as lead-acid, but they are extremely tolerant of discharge, they are hard to
ruin. Many offshore sailors including myself use 6V golf cart batteries
which are designed to put out a moderate constant current for A LONG TIME.
You can wire two in series to give you your 12VDC. Just for fun, another
type of battery is the AGM, or associated glass mat. They are the best of
gel cells AND wet cells; they were developed for use in fighter jets where
they are often upside down and subjected to multi-G forces. They are,
unfortunately, also extremely expensive and hard to come by.

Question 2. Where can I find articles & schematics for a solar cell to
provide a trickle charge for the aforementioned battery?

Google for solar chargers, they are available at most marine stores too and
not particularly expensive. I'd guess buying one would be considerable
cheaper and more reliable than what you might be able to build.

Thank you very much.

Cordially,
west