How should batteries be stored for a long period?

Before storage, batteries must be fully charged. If they are inside a UPS, it is best to disconnect them or switch the unit off completely so that its electronics do not slowly drain them. The ideal place is cool, around 15–25°C, dry and out of direct sunlight.

Recharging every 6 months applies to a cool place. In a hot storeroom, for example a loft or a container in summer, self-dischargeGlossary · BatteriesSelf-dischargeThe gradual loss of charge in a battery kept in storage without use, caused by internal chemical reactions. speeds up and recharging is needed more often, roughly every 3 months. If you have many batteries, mark each one with the date of its last charge.

A practical check is measuring the open-circuit voltage with a multimeter. For a 12 V lead-acid battery, a reading of around 12.7–12.8 V indicates a full charge, while below about 12.4 V it needs charging soon.

The most common mistake is storing a UPS or battery half-empty, after an outage or a test, and forgetting it for months. Sulphation then permanently reduces capacity, and the battery may never recover.