Originally Posted by camaraderie
Absent a phantom load...a lead acid battery will self discharge at about 10% a month. More when the temps are above 75...less when they are freezing.
The best thing to do is to make sure your batt is fully charged...then disconnect it with the $5 switch and you can safely walk away for 90 days before you recharge it. This is better for the battery than leaving it constantly on float charge AND you won't have to worry about checking water levels between charges.
Lead acid batteries self-discharge up to 1% per day; age is a factor, too. They will also begin to sulphate once they get below 95% which is why you don't want to go more than a month - even that is pushing it for an old battery in warm temps.
90 days is way too long, that will quickly kill a battery, with the only exception when it is 20 degrees outside. Then you can go 2-3 months.
I prefer to use an external fuse as a cutoff so I don't have to open up the battery box.