Which batteries are available for boats?

To power important devices such as navigation systems, interior lighting and refrigerators, the battery must be powerful. Depending on the intended use, different battery technologies can be considered for use on boats.

Marine battery technologies in detail

1. the classic wet batteries for boats and yachts

Battery manufacturers have been constantly developing wet batteries since their invention, and today the main argument for buying them is the low price. Hydrogen and oxygen are produced during charging, which escape through a valve in these closed boat batteries. To refill with distilled water, the battery must be easily accessible.

Current lead-acid batteries are low-maintenance and have low gas emissions. Thanks to their medium vibration resistance and tiltability, you can use them on your boat. For optimum durability, wet batteries may only be discharged to 50 percent. Closed wet batteries can emit gas during charging. During this secondary process, water from the electrolyte is broken down into water and oxygen. Depending on the model, it may be necessary to top up with distilled water, with the exception of maintenance-free batteries (MF).

2. gel batteries for boats & yachts (VRLA)

Gel and AGM batteries are referred to as sealed lead-acid batteries (valve-regulated lead-acid battery, VRLA) due to their characteristics.

With a gel-like electrolyte, they are a further development of sealed batteries and do not gas during normal operation. VRLA batteries require no maintenance and can also be operated in an inclined position. If handled properly, they can withstand several cycles. Severe overcharging leads to irreversible damage.

Gel batteries bind the actually liquid electrolyte with silicic acid, the electrolyte is no longer liquid and is in a gel-like state. This means that operation in an inclined position is unproblematic. Batteries based on gel technology are capsize-proof, maintenance-free and cannot leak. The main advantage over AGM batteries is the lower self-discharge.

Water decomposition is almost completely reversed internally (recombination). In the event of overcharging (e.g. due to excessive charging voltage), recombination is suspended and the integrated pressure relief valve is activated to release the gases. Due to their relatively high internal resistance, they are not suitable for starting the engine, so gel batteries are only used on boats as supply batteries batteries. Deep cycle batteries are often used for electric outboards as they are perfect for this application due to their cycle stability. Deep cycle batteries are virtually the perfect marine batteries and fulfill all requirements such as low self-discharge and high cycle stability.

The sealed AGM batteries (absorbant glass mat) integrate modern and contemporary technology. Glass fiber fleece binds the electrolyte, the glass fiber mats are located between the plates and absorb the acid. These boat batteries are therefore leak-proof, maintenance-free and can be installed in any position, just like gel batteries. Pressure relief valves are also included for safety reasons and are triggered in the event of severe overcharging. As with gel batteries, frequent overcharging leads to an irreversible loss of electrolyte fluid and should be avoided as far as possible by using chargers.

Since batteries based on AGM technology can deliver high currents, they are suitable for energy-intensive consumers such as electric anchor winches and bow thrusters.

3. lithium iron phosphate batteries for boats & yachts (LiFePO4)

Lithium iron phosphate batteries are in a league of their own and outperform lead-based batteries in various disciplines.

Mostly manufactured for cyclical use lithium iron phosphate batteries with state-of-the-art lithium technology have been replacing lead-acid, gel or AGM batteries for some years now. Selected models can also be used as traction batteries.

The LiFePO4 batteries score points with their enormous efficiency, ultra-short charging times and advanced battery management system.

Compared to wet, AGM and gel batteries they deliver more power, are much smaller and lighter and therefore have a significantly higher power-to-weight ratio. LiFePO4 batteries can withstand deep discharges of up to 100 percent and up to 5,000 charging cycles - that's 5 times longer than the best AGM batteries! The purchase price is currently still relatively high, but over the years, lithium iron phosphate batteries will impress with their excellent price-performance ratio. Supply and demand are constantly increasing. Due to their low weight and space requirements, they are also particularly suitable for small and medium-sized boats.

Which boat battery do I use for the different purposes on the boat?

The batteries differ in terms of the possible amount of current, number of cycles, capacity and safe depth of discharge due to the technologies and the respective design.

• Pure starter batteries are designed to deliver maximum energy for a few seconds. When selecting a battery, pay more attention to the cold-start current than to the capacity. Today's small models deliver higher starting currents than earlier variants. For maximum durability, you should not use more than 15 percent of the battery's capacity.
• Consumer batteries deliver a lower amount of current over a long period of time. They can be discharged to around 50 percent without damage. Consumer batteries are the standard on boats and are important for navigation devices and on-board electronics.
• Combination batteries can be used as starter and consumer batteries and are a convincing compromise.
• Drive batteries power an electric motor. They can withstand discharges of up to around 75 percent

How important are the charging cycles for boat batteries?

In the product descriptions or manufacturer's specifications, you will sometimes find information on the cycle stability. For many boat and yacht owners, a consumer battery with around 500 cycles is sufficient.

Example: If you spend a day on your boat or yacht about every other weekend per year, this means around 25 charging and discharging cycles. If you also go on a two-week trip, this adds up to 14 cycles. This results in just under 40 cycles per year and 400 charging cycles in ten years. Models with 500 to 600 cycles at 50 percent discharge meet these requirements.

Long-distance sailors have higher demands on the on-board supply - a charging and discharging cycle takes place every day. As a result, normal consumer batteries reach the end of their service life after around two years. For daily use, it is advisable to purchase a boat battery with a cycle count of more than 1,000. Modern lithium batteries are ideal here, as they can also withstand several years of sailing around the world.

What power rating does the battery need for my boat/yacht?

In addition to the battery technology and the application or intended use, the purchase decision also depends on the required power rating. Use the following calculation to determine the required total capacity of the marine batteries: 1. consumer power / battery voltage = required current in amperes 2. required current in amperes * switch-on time of the consumer = required ampere hours 3. required battery capacity = required ampere hours * safety reserve (factor of around 1.5 for lead batteries)

Calculation example for an electric motor with 200 watts:

200 watt electric motor / 12 volt battery voltage = 16.66 amps 16.66A * 6 hours operation = 99.96 Ah 99.96A * 1.5 reserve = 149.94 Ah battery capacity

To drive a boat with a 200 watt electric motor for six hours without a break, you need a battery with a capacity of 150 Ah. Repeat the calculation for the various consumers to determine the total power required for your boat.

Also think about the weight

A higher capacity means a higher weight. An AGM supply battery with 150 Ah weighs around 40 kg. Installation, removal and transportation are correspondingly difficult. Modern lithium batteries with 100 Ah only weigh around 15 kg and provide the performance and endurance of an AGM or gel battery with 180 Ah.

Note: Chargers for gel, AGM and LiFePO4 batteries cost approximately the same.

Summary

If the purchase price is the decisive selection criterion, then invest in a classic wet-cell battery. However, these do not last as long, require frequent maintenance and must not be installed horizontally.

• Gel batteries are superior to wet batteries, but are only suitable as supply batteries and usually have a slightly longer service life than AGM batteries.
• AGM batteries are the right choice for many boat owners due to their installation position and low internal resistance and can be used in a variety of ways.
• Lithium iron phosphate batteries offer the same advantages in terms of safety and installation options as AGM batteries and at the same time a significantly higher energy density and service life. Over the years, the additional investment in a high-quality lithium battery can therefore pay off.