This article originally appeared in Light Plane Maintenance, Dec. 2005.Aircraft starting batteries have a tough life; much more so than their automotive counterparts. They are left idle for days or even weeks at a time, then asked to start a 500 cubic-inch engine in cold weather with three gallons of oil the consistency of molasses in the sump. To make matters worse, aviation batteries have significantly lower capacity than an auto battery, and multi-weight oil can help only to a degree. Twenty-four volt batteries provide some help in high-current-demand situations such as speeding up electric retractable landing gear, but in terms of battery cost compared to 12 volts, a 24-volt system leaves a lot to be desired on cost vs. benefits. When left idle, batteries self-discharge about one percent or so a day due to the side effects of components (antimony) used to keep battery-grid structures from shedding and damage during use. This self-discharge process has a long-term, deleterious effect on the battery if not corrected by frequent recharging. The term is sulfation, and when left unchecked it means the gradual self-destruction of the battery. Recharging and the replacement of lost electrolyte, a natural process in wet-cell batteries, staves off permanent sulfation. When a battery is allowed to remain in a state of sulfation, either from lack of use or from lack of recharge, it tends to lose both capacity and life. Initially reversible sulfation hardens with time and it becomes less and less reversible. As sulfation flakes off and falls to the base of the case, it can short out the cells.