Stanley 50 Amp Battery Charger/ Maintainer With LCD Screen. 50 Amp Engine Start helps to start most vehicles up to V8. Battery Chargers restore energy via a continual electrical current. 3A maintainer keeps the battery at optimum level by charging as needed. Push button selection for 12V Lithium or 12V Lead Acid battery charging. Charging automatically stops when battery is fully charged or topped off and switches to float mode monitoring to maintain charge. Tests alternator to determine operational performance. Provides reverse polarity protection to ensure that jumper cables are connected correctly. Informative screen with icons lets you see operation and charging status.