I don't know where your numbers come from - the OP didn't mention a battery
size.

But more importantly, your number of 80 AmpHours for 3 months implies about 1 AH
per day, This cold be handled by a 5 Watt panel such as this one featured on
the Boat/US site. It has a built in diode.

http://www.boatus-store.com/webapp/w...roductId=56290

Since the winter sun is not very strong, and the sky might be cloudy, this might
be on the small size for a larger bank, so you would be well advised to visit
monthly to make sure they are staying charged.

You might consider getting a "full size panel" and a regulator. These will
collect enough light even through shrink wrap to keep a large bank charged, and
will be useful in the summer.

"Lloyd Sumpter" wrote in message
...
On Sun, 23 Nov 2003 16:06:53 +0000, Hmseconomy wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up? Can a single small trickle charge panel charge
two
batteries at the same time? What's the recommended connection method? Need
a
diode to protect against overcharging (even with a minimum output panel?).
Any
advice would be appreciated.

I'll start with an assumption that may be wrong, but...Assume a battery loses
50% of its charge in 3 months, and it's about 80AH. That means it loses about
..4
AH per day. So it needs about .4 amps CONTINUOUSLY to keep it charged.

Now, since a solar panel only puts out anything about 50% of the time (assume
full sun all day) you would need an 800mA panel. But a "1 Amp" panel only puts
out close to 1 amp in full sun when the sun's directly perpendicular to the
cell, I'd put it a 60-70% "fudge factor" (more if you live in a cloudy area).
This means you need about a 1.3A panel per battery.

Note that most of these "trickle charge" solar panels only put out 200mA or
so.

Also, a diode is so that the battery doesn't "backfeed" the panel, not to
prevent overcharging.

Based on this, I'd say you'd be safe with a 2A panel, paralleled to both
batteries (assuming there's no load on the batteries). I've used a 2A panel on
one 4D battery over the summer, and it seemed to work well. I doubt one of
these
"trickle charge" panels would be useful for the long term.

Lloyd Sumpter
"Far Cove" Catalina 36