Batteries on board the boat – Types, battery banks, and safe installation

A complete guide to marine batteries: AGM, GEL, and wet-cell batteries, how to build battery banks, and connect them correctly for maximum safety and performance.

All electronics on board a boat need power, and it usually comes from a battery. Battery requirements vary depending on the boat's size, equipment, and energy needs. Some boats have multiple batteries and battery banks, while smaller boats often manage with a single battery.

Types of batteries for boats

Most marine batteries are based on lead-acid technology, where the battery contains lead plates, lead oxide plates, and sulfuric acid as electrolyte. The most common types are:

• Wet-cell battery: The plates are submerged in sulfuric acid.
• AGM battery (Absorbed Glass Mat): The acid is absorbed in fiberglass mats between the plates.
• GEL battery: The electrolyte is mixed with silica to create a gel structure.

There are also other battery technologies, such as lithium, but the above are the most commonly used in recreational and commercial shipping.

What is a battery bank?

A battery bank consists of several batteries working together to provide sufficient capacity. Larger boats often have several banks, for example:

• House bank: For lighting and electronics on board.
• Engine bank: For engines and generators.
• Emergency bank: For critical systems such as VHF radio and AIS.

Safe installation of batteries

Batteries should be installed in a dry, safe, and easily accessible location for maintenance. Important guidelines:

• Install near a ventilation opening – wet-cell batteries emit hydrogen gas during charging.
• Never above or below fuel tanks or filters.
• The battery must be firmly mounted – no movement is allowed (max 2.5 cm).

Connect the battery correctly

The wire gauge (AWG) depends on current consumption and battery capacity. Follow NMEA standards:

• All bare wires must be tinned.
• Maximum four conductors per battery terminal.