[Kevin Sevcik]

Third question: Have you left your deeply discharged batteries sitting around for hours at a time?

The primary enemy of lead acid batteries is sulfation. When you discharge a lead acid battery, the lead turns to lead sulfate. If left to sit long enough, the lead sulfate will crystallize into a very hard form that just won't dissolve again. Thus you end up losing reactants, and you battery holds less charge. Any battery below 11V is in actual danger of sulfation. The more dead the battery, the faster the sulfation. Plus, batteries discharge themselves over time. If you just leave them sitting about over the summer, they'll discharge and sulfate. The obvious solution is a well planned strategy for maintaining your batteries.

High heat is a seperate problem. That could potentially boil off some of the electrolyte and dry out the battery.