‘Sandpiper’ is laid up in my garage. She’ll remain there until the spring where she should be protected from the elements, but I shall have to take note when there is a cold spell, because if it is exceedingly cold, the electrolyte* in the ship’s battery could freeze. I shall need to periodically discharge the battery and recharge it. The reason for this is to keep the battery plates from being clogged with lead sulphate, and if a battery is not charged, eventually it will completely discharge itself. Ideally, it should not be allowed to discharge to a point where it has less that 25% charge.
Two days ago I set about discharging ‘Sandpiper’s’ 12 volt battery that normally powers two handheld GPS units, an Autohelm 800 and an iPhone 400s. After discharging it overnight and into the following morning my voltmeter read 9 volts. The system I use for discharging the battery is to attach it to three 12 volt 0.183 amp bulbs wired together in parallel. For recharging I have an old-fashioned Selmar ‘Star’ 240 volt mains charger.
*Composed of 35% sulphuric acid and 65% water solution.
12 Volt Battery Maintenance
Battery Basics: A Layman’s Guide to Batteries
Lead Acid Batteries