The Battery Tender Battery Charger 021-0123 is a compact and versatile battery charger designed to keep your 12-volt lead-acid batteries fully charged and maintained. It features a 4-step charging program that automatically switches between charging mode and float mode to prevent overcharging. The charger also has a safety timer to prevent damage to the battery in case of a power outage. It is compatible with all types of lead-acid batteries, including flooded, AGM, and gel batteries. The charger comes with a quick-connect harness for easy and convenient use, and it is also spark-proof and reverse-polarity protected for added safety. With its compact size and advanced charging technology, the Battery Tender Battery Charger 021-0123 is an ideal choice for keeping your batteries in top condition.