Plates are made of lead and calcium and some tin may also be used. Because there is no antimony in the grids, self-discharge is quite low. Fully charge the batteries before laying up the system for the winter, and apply at least one full charge during the winter. Gel Batteries Gel batteries have the lowest rate of self-discharge, and can be left months without a charger attached. Just be sure to bring the batteries to a full charge before leaving them.
Many systems have two different types of batteries for house and starter.
Follow the recommendations for the type of battery that requires the most charging during the winter. If you leave a charger hooked up, it's permissable to connect all the batteries in parallel. If your area is subject to frequent power outages, be sure to check charger operation frequently, since it isn't a good idea to have different battery types connected unless they are being charged. Often, there are a number of small loads on the batteries such as clocks, instrumentation, and control panel indicators. If you're going to leave the batteries without a full-time charger attached, then it would be wise to lift one of the battery leads to make sure that there are no stray loads discharging the batteries.