Originally Posted by 5picker
Yep... a fully charged and then properly disconnected battery will NOT freeze unless it gets somewhere south of -70º and will only loose about 40% of its charge in 4-5 months.
Charge it up and leave it right where it is.
I kind of went a different route which I highly recommend if there is 120 Vac available.
All that's been mentioned does "freeze proof" a lead acid battery but it doesn't halt sulfation. If a battery is discharged ANY amount (and all lead acid batteries self discharge) lead sulfate is formed. That's just how lead acid batteries work. The longer the sulfate remains the harder it is to convert it back to lead and the sulfuric acid/water electolyte.
Yes, the battery may only have lost 40% of it's charge (some more, some less) but fact is that not all of the sulfate will be removed as it may have sat there for 6 months.
To prevent this I preferred (past tense as I now have Lithiums) to use the converter to maintain the batteries. If not the converter than at least a battery maintainer sized to the size of the battery bank. Large enough to replace all that is lost by self discharge. Average self discharge can be ~5% per month at average temps. More when hot, less when cold but never none. If you want maximum life, and full capacity, you can't really let a lead acid battery sit in any partially charged state.
I suspect that those who are getting the long life out of their lead acid batteries are maintaining them at full charge at all possible times and just checking water regularly.