The bfs Plugs:
A Synthesis of Technology and Design

Tried and Tested: Plug III

This robust battery watering plug can be used in nearly all applications and with a wide range of filling pressures. The self-cleaning mechanism inside the plug is designed to control the shut-off valve precisely and reliably for many years – even in the toughest circumstances. Plug III meets all the requirements that are standard for high-quality watering systems today. Its versatility, reliability and robustness, and no less its many patented construction details make the plug what it is today: the leading product in the battery industry worldwide.

Discover the Main Features of Plug III

bfs Logo

The bfs logo is your guarantee of authenticity and as such proves that the quality of the product knows no compromise.

Inspection Opening

The inspection opening allows for easy measuring of acid density at the flip of a lid. Closing the lid of the plug completely seals the opening.

Water Trap

A generous water seal created with a trap that is integrated in the plug prevents intercell flashovers (university certification).

Dual Chamber System

The plug’s two-chamber system keeps gas and water separate. In this way, the self-cleaning mechanism is protected from dirtying and remains highly reliable.

The Labyrinth

Hydrogen gases that leave the cell are deflected several times in the plug’s gas compartment, condensing on its walls. Most of the condensation is directed back into the cell. The result is a dry, acid-free and clean battery top.

Lever-Controlled Valve

Controlled via reversed lever action, the shut-off valve opens and closes with 2.5 times the buoyant force/weight of the float. This patented system has proven its reliability for 30 years.

Decompression System

To decrease the pressure build-up in the system during the watering process, all bfs plugs have a time-controlled closing mechanism that automatically reduces water pressure into the cell. Since this process does not involve any peripheral components, operating errors are impossible.

Level Indicator

A clear indicator makes it easy to determine the exact electrolyte level.

Compact Design and a Perfect Choice of Materials

A casing made of impact resistant polypropylene offers outstanding protection for the plug in rough industrial settings. The use of modified polycarbonates for the interior has proven an ideal complement. The material ensures that all moving parts work together perfectly.

Wide Range of Filling Pressures

The bfs plug can be used with any filling pressure, using any method of watering imaginable (0.2 to 3.8 bar or 2.9 to 55.1 psi). This means that no additional components such as pressure regulators are necessary.

Your Corporate Design

You can have bfs plugs show your logo or your company colors. Completely acid resistant, the generous upper surface of the plug’s lid can be foil stamped or engraved to your specifications. You can even have the lid itself made in your company color.


bfs plugs can be delivered with preinstalled adaptors. These range from S35 push-in, to different bayonet models and threaded connections, to custom designs. bfs can make plugs that fit any battery vent. To allow for proper alignment of the plug on the battery, the plug base can be turned on the adaptor by 360° (bfs patent).


Our unparalleled variety of floats allows you to attain perfect electrolyte levels in any type of battery and in any area of application. Floats are available separately and preinstalled.

Plug Series III and IV

The bfs Plug: Convincing Quality

Safety Knows No Compromise

Convincing quality also means the highest level of safety. The many safety features built into bfs plugs along with patented filling and shut-off mechanisms contribute to the high performance of batteries for many years.

  • An integrated water trap prevents intercell flashovers.
  • Our patented injection system and precision mechanisms ensure exact electrolyte levels and prevent escape of battery acid due to overfilling.
  • The dual-chamber system keeps gas and water separate. The plug’s mechanism is protected from dirtying and the system remains reliable for many years.
  • An automatic decompression system makes sure the bfs watering system is always ready for operation. It protects from mishandling and makes additional equipment unnecessary.
  • The use of brand plastic materials that are resistant to acid, temperatures and high impact guarantee the highest possible operating life of the plugs.

Cost Efficiency

  • Using an automatic watering system maximizes the life expectancy of your batteries while considerably reducing labor input for watering.
  • The labyrinth optimizes condensation and returns water to the battery, thus making the intervals between watering longer.
  • The new patented injection system designed for Plug IV makes for even faster filling and an extremely broad filling pressure range of 0.2 to 3.8 bar (2.9 to 55.1 psi). No pressure regulator necessary.

Outstanding Quality

  • All bfs components are manufactured according to DIN ISO 9001:2008.
  • Extensive in-process functionality tests are carried out at high and low pressure.
  • A complete verification follows the production process: before leaving the facility, each plug undergoes detailed quality and functionality testing and is marked with a date code.
  • All peripheral products undergo ongoing stress and fatigue tests to verify their quality.

Plug IV – The New Generation

Plug IV was developed to complement the extremely successful bfs Plug III. With its installation height reduced by 12.5 mm (bayonet-, clip-in and threaded version), Plug IV can be installed as part of an automatic watering system even when there is little room above the battery.

Plug IV is a new design that reflects bfs’s experience of more than 30 years. A new, patented injection system causes the water to swirl as if in a vortex, virtually pulling the water through the plug. As in the still eye of a tornado, the water is calm when it meets with the shut-off valve. This nature-inspired trick allowed us to increase the precision of the closing characteristics even further.

Regardless of the filling pressure (0.2 to 3.8 bar / 2.9 to 55.1 psi), the plug controls the electrolyte level very exactly. Battery acid is securely contained by the plug and will not spill, as might be expected when batteries are used in off-road vehicles. This makes Plug IV ideal for smaller, off-road electric vehicles such as golf carts. Even with the reduced height of Plug IV, all of Plug III’s well-proven features have been retained. Emphasizing the plug’s functionality, the decidedly compact design of Plug IV and its use of innovative technology were recognized when the product received the iF product design award.

  • Main Features

  • • “Low profile”: extremely low clearance
  •  New, patented injection system allowing faster filling
  •  Exact, consistent electrolyte levels regardless of filling pressure
  •  Cell content of small battery blocks will not spill
  •  Winner of the prestigious iF Design Award