Small (5W) solar panel does work to keep batteries okay

The curve is NOT linear, nor is it the same for differing density of electrolyte. Temperature makes a significant decrease in electron and chemical activity BUT BUT BUT BUT BUT sulfation still can form and still can lattice at -20C

A typically abused forgotten battery (disconnected not top charged) does not uniformly sulfate the surface area of a plate. Latticed sulfation is like cancer, a spot can form and then render the area inactive. A loss of capacity in percentile. But newer sulfate that joins with the latticed old sulfate is much more easily and quickly rendered "hard" and difficult or impossible to remove unless steps are taken at appropriate time spans to revert the sulfation back into solution.

The process is slower with Pb only plates, or lead calcium.

Another reason to hasten the development of lithium technology.

Here is a Trojan document that may help.

Look at the self discharge rates for 86F and 42F, or .0075/wk and .0015/wk respectively.

Note that when the temperature was halved, the discharge rate was 1/5. If you halve the temp again to say 21F, doesn't it stand to reason the discharge would be reduced by 1/5th again?

That gives 1/25th of the 86F rate of .0075, or .0003/wk.

Given 28 weeks in Nov-May x .0003 is a drop is SG of .0084SG, and a drop to 1.28 - .0084 = 1.276.

The fully charged table allows that 1.250 is freeze proof down to -62F.

Think about an AGM that starts at 1.3SG and has a much lower self discharge rate. How many years?

HTH;
John

Absolute zero would work, but the electrolyte would freeze ;)

How cold does a battery have to be to have no self discharge and is there a difference between the 6V and 12V as far as that temperature is concerned? First I've heard of this. Thanks much.

renoman69 wrote:
The OP is in "OTTAWA CANADA".....can you spell -35 degrees..... only a fool would let his expensive batteries sit for 6 months in those kind of temps.

If the battery is going to freeze when fully charged, it doesn't matter how many watts of solar are used. :)

A cold battery will have a nil self discharge rate.

If stored indoors, how is solar going to work?

HTH;
John

I suspect you just have good batteries. I have 405 watts of solar and see very little output on winter days without snow on them.

The OP is in "OTTAWA CANADA".....can you spell -35 degrees..... only a fool would let his expensive batteries sit for 6 months in those kind of temps.

At Lat 45, as you would find in Ottawa, ON, Canada, any type of battery can sit disconnected between Nov and May due to low ambient temps.

No solar of any Watts are needed.

HTH;
John

From what i have been reading lately, Even though they will discharge slowly, sitting that long is really hard on the batteries. Any tiny charge even below what it takes to float them is tremendously better for reducing plate corrosion, loss of capacity and hard sulphation, than leaving them alone for a month or more.

Jim

If your batteries are in good shape, you can expect them to still be at a near full charge after 6 months as long as you remove any parasitic draw from them. Simply remove the ground cable.
I have a '57 Ford in storage and it only gets started twice a year and driven only once a year. The battery stays charged and even with the mechanical fuel pump and carb it takes 15 to 30 seconds for gas to get to the carburetor before it starts.