Solar and Marine Batteries

I was hoping someone could help me with a Solar panel problem. I have a 15W solar panel hooked to a deep cycle marine battery. This powers some lights and an inverter for power in my tool shed. It works perfectly in the summer and in most cases I can have the battery back to full power in only 1 to 2 days after heavy use. It is hooked up with a charge controller to prevent over charging.

However last winter the cold weather killed the battery and the battery was only 1 year old. This spring I replaced the battery so my new battery is only about 7 months old. Its an Autocraft Marine 460CCA. It turned cold here and frosted the 2 nights ago and I had made a trip out to my shed only to find the battery seemed almost dead it wouldnt even power my lights. My lights are only low volt led's.

Whats going on I thought Deep Cycle Marine was designed for that kind of application? But the first signs of cold weather is practically killing the battery. The setup works perfect till cold weather then all of a sudden the battery seems to die. Its getting plenty of energy from the panel to maintain and/or charge it even in the full of winter. But something about this setup isnt working right as far as the battery is concerned when the weather turns cold.

That battery was like $70 so being economical with the solar panel isnt working replacing the battery every 8 to 9 months. What could be my problem? Do I need a different kind of deep cycle battery?

Greetings angles, welcome to the Forum !

Gees, that's a toughie, and I'm going to take a shot in the dark with it.

You say...
"Its getting plenty of energy from the panel to maintain and/or charge it even in the full of winter."

You sure?, you checked it with a Voltmeter and KNOW that it's up to voltage!

Try removing everything (a physical disconnect) of everything except the Charging Circuit. Let the Charger get it up to full charge.

Then, disconnect the Charging circuit, leave the Voltmeter on the Battery, and reconnect the lines to your circuits, WITHOUT turning anything on. If you have more than one, connect them one at a time.

What I'm trying to do, is see if there is a drain via the connecting wire. Something that (when cold) is shrinking and maybe touching (barely) something else that could cause this.

Now, do you see a Voltage drop ? If so, check your routing of your circuit wire, and see if something is pinched or frayed across a sharp metal edge.
I'm just guessing now at the possibilities. You just need to look at it a piece at a time, there's got to be some little thing that's wrong.

Be nice if you had Ampmeter, where you could check the loads individually.

Anther way is to remove the Light from the end of the line, and disconnect the wire from the battery, then do a resistance check with an Ohmmeter, to see if there is any path between the wires, or to ground from either wire.

Best I can offer, see what you can do with this, and get back to us !

Have a good Day !
S.W.