BLACK+DECKER BM3B 6V/12V Automatic Battery Charger & Maintainer — 1.5A, Clamp and O‑Ring Terminals

The BLACK+DECKER BM3B is a fully automatic 6V/12V battery charger and maintainer that safely charges AGM, GEL and wet batteries and then holds them at optimal voltage without overcharging.

Designed for seasonal vehicles and equipment, the BM3B delivers a steady 1.5 amp charge and automatically switches to a float-maintenance mode once a battery reaches full capacity. It supports both 6- and 12-volt systems, connects via alligator clips or O-ring (ring) terminals, and includes built-in protections so you can leave it attached during storage with confidence.

How do I pick the right voltage and connect the BM3B?

Select either 6V or 12V using the slide switch—match the charger setting to your battery’s rated voltage before connecting. Use the included cable clamps for quick hook-up or the O-ring terminals for a permanent, weather-ready installation. Make sure connections are clean and secure to avoid sparks or false readings.

• Slide voltage selector to 6V or 12V to match battery.
• Use clamp leads for temporary charging; use ring terminals for long-term mounting.
• Observe polarity: red to positive, black to negative.

What protections and safety features does it have?

The BM3B includes automatic shutdown and float-mode monitoring so charging stops when the battery is topped off, then maintains charge without overcharging. Built-in circuitry guards against reverse polarity, short circuits and excessive current. The unit is ETL certified, meeting independent safety and performance standards.

• Automatic stop and float maintenance to prevent overcharge.
• Reverse-polarity and short-circuit protection for safe operation.
• ETL certification for verified safety and reliability.

Which battery types and vehicles does this charger support?

The BM3B works with 6V and 12V AGM, GEL and flooded (wet) lead-acid batteries commonly found in a wide range of vehicles and equipment. It’s suited for small and medium battery capacities that accept a 1.5 amp charge rate, making it ideal for seasonally stored assets. Avoid using it on lithium batteries unless the battery manufacturer explicitly permits a charger of this type.

• Compatible with AGM, GEL and wet lead-acid batteries.
• Common applications: motorcycles, lawn mowers, ATVs, snowmobiles, boats, RVs, classic cars.
• Not intended for standard lithium battery chemistries unless specified safe.

How is the BM3B mounted and where can I store it?

The charger has an integrated mounting bracket for wall or bulkhead installation inside garages or storage compartments, keeping it off damp floors and away from moving parts. Its compact footprint lets you position it near battery terminals with the ring terminals connected for seasonal maintenance. Store the unit indoors or in a dry, ventilated area when not in use.

• Built-in bracket for secure wall or compartment mounting.
• Compact design saves space in garages and RV bays.
• Use ring terminals for longer-term attachment and clip leads for temporary charging.

Who is this for? The BLACK+DECKER BM3B is aimed at owners of seasonal or stored vehicles and equipment—classic cars, motorcycles, boats, lawn and garden machines, ATVs and RVs—who need a low-maintenance, safe way to keep batteries healthy over weeks or months. It's also a practical choice for hobbyists and small-fleet managers who want a reliable 1.5 amp charger with simple controls, built-in safety features, and versatile connection options. Designed to be user-friendly, it’s an accessible solution for DIYers who prefer a set-and-forget approach to battery maintenance.