Types of Marine Batteries

Types of Lead Acid Batteries

There are three types of lead acid marine batteries. These include the flooded batteries (including sealed / value regulated), gel batteries and Absorbed Glass Mat (AGM) batteries. These are rated depending on the energy output measured in ampere hours. The output, together with the lifespan, is what typically dictates the price of the batteries. 

Lithium batteries are the subject of a seperate post.

Flooded Battery

These are also called wet batteries, and are the cheapest and most common type of marine batteries. When the battery is being charged, the sulfuric acid produces oxygen and hydrogen, which escape through the vents. These batteries need periodic inspection and topping up with distilled water. The flooded batteries are known to self-discharge at a rate of 6%-7%, which is higher than with AGM and gel batteries. These batteries are difficult to maintain in boats as they tolerate minimum vibrations and need to be kept upright at all times.

Sealed Battery

This term can refer to a number of different constructions, including only a slight modification to the flooded style. In that case, even though the user does not have access to the cell compartments, the internal structure is still basically the same as a flooded battery. The only difference is that the manufacturer has ensured that a sufficient amount of acid is in the battery to sustain the chemical reaction under normal use throughout the battery warranty period. Other types of lead acid batteries are also sealed see below. Very popular uses are engine starting and limited starting/deep cycle applications.

Typical absorption voltage range 14.2 to 14.7 volts.

Typical float voltage range 13.1 to 13.4 volts.

VRLA (Valve Regulated Lead Acid Battery)

This is also a sealed battery otherwise know as sealed lead-acid or maintenance free. The valve regulating mechanism allows for a safe escape of hydrogen and oxygen gasses during charging. There are three primary types of VRLA batteries, sealed VR wet cell, absorbent glass mat (AGM) and gel cell.

The term “maintenance free” is a misnomer as VRLA batteries still require cleaning and regular functional testing. They are widely used in large portable electrical devices, off-grid power systems and similar roles, where large amounts of storage are needed at a lower cost than other low-maintenance technologies like lithium-ion.

The term “maintenance free” is a misnomer as VRLA batteries still require cleaning and regular functional testing. They are widely used in large portable electrical devices, off-grid power systems and similar roles, where large amounts of storage are needed at a lower cost than other low-maintenance technologies like lithium-ion.

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VRLA batteries have a pressure relief valve. Valve activation, due to hydrogen gas increasing in pressure during recharging, allows some of the gas or electrolyte to escape decreasing the overall capacity of the battery. Rectangular cells may have valves set to operate as low as 1 or 2 psi; round spiral cells, with metal external containers, can have valves set as high as 40 psi.

Typical absorption voltage range 14.2 to 14.5 volts.

Typical float voltage range 13.2 to 13.5 volts.

Gel Battery

The “gel” is a combination of pure water, phosphoric acid, sulfuric acid and fumed silica. This gel is viscous helps prevent the battery from leaking if tipped or damaged. These are sometimes referred to as “silicone batteries”.

This type of battery is also called a “recombinant battery”. This is because the hydrogen and oxygen produced during charging is converted back into water by internal pressure.

Typical absorption voltage range 14.0 to 14.2 volts.

Typical float voltage range 13.1 to 13.3 volts.

Absorbed Glass Mat (AGM) Battery

AGM (Absorbent Glass Mat) batteries feature fiberglass mesh between the battery plates that are saturated in an acid-electrolyte solution. Pressure valves allow oxygen that is produced on the positive plate during charging to move to the negative plates, where it recombines with hydrogen to make water. These batteries have better vibration and shock protection compared to gel and flooded batteries. Although they are more expensive than the others, the added cost is well reflected in the quality.

AGM batteries present better self discharging characteristics than conventional batteries in different range of temperatures. As with lead-acid batteries to maximize the life of AGM battery is important to follow charging specifications and a voltage regulated charger is recommended and also there is a correlation between the depth of discharge (DOD) and the Cycle life of the battery, with differences between 500 and 1300 cycles depending on depth of discharge.Typical absorption voltage range 14.4 to 15.0 volts

Typical float voltage range 13.2 to 13.8 volts.

Did you know?

98+% of all battery lead is recycled compared to:

  • 55% of aluminium soft drink and beer cans
  • 45% of newspapers
  • 26% of glass bottles
  • 26% of tyres

Lead-acid batteries top the list as the most highly recycled consumer product.

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