- Power on the water -
A marine battery is the most important electrical component in your on-board power system. When the engine is not running and no other energy sources are available, such as a wind generator or solar power system, the boat battery is the only energy source to supply all electrical devices on board. Since most boats and yachts are equipped with extensive and high-quality electronics, a complete battery failure would result in a real maritime emergency.
The types of marine batteries available are just as varied as their intended use. On board you will find
Boat engine starter batteries
Batteries for starting the boat engine, also known as starter batteries or car batteries have to provide high current for a short time. Only a small amount of energy is drawn during the starting process and quickly recharged when the engine is running.
Boat consumer batteries
Batteries that are used to provide power to electrical consumers (lights, navigation instruments, fridges, etc.) are known as consumer batteries or 'house' batteries. In recreational vehicles or in caravans they are also called leisure batteries. Consumer batteries for boats are used cyclically. This means that they are regularly discharged more than a starter battery. They have a greater depth of discharge, also known as DOD.
Bow thruster & winch batteries
A bow thruster or winch battery supplies power to the bow or stern thruster or the winches on board. It has to provide a lot of power at short-duration and is therefore comparable to a starter battery. As the running times are longer with bow thrusters or winches than with starters, more energy is drawn from bow thruster/winch batteries. Bow thruster manufacturers define a minimum capacity that should be observed. If you want to use a lithium battery to power bow thrusters and other DC motors, check with the manufacturer first. Because LiFePo4 batteries have a high energy density, there is less voltage drop, resulting in a higher current for the relay when starting the bow thruster and during operation. This may result in motors burning out.
Batteries for electric outboard engines
Electric outboards require no fuel and are powered by a lead/acid rechargeable battery or by lighter and more powerful lithium batteries.
Boat batteries for multiple applications
There are cases where there is no separate bow thruster battery or winch battery. In these instances, the bow/stern thruster or winch is connected to the boat's consumer battery. In other cases, bow/stern thrusters or winches are connected to the boat's starter battery. This must of course be taken into account when selecting the type of battery and battery capacity.
Nowadays a distinction is made between lead acid and lithium technology for marine batteries.
Lead-acid batteries include traditional serviceable (flooded) and maintenance-free (sealed) wet batteries with liquid electrolyte (water-diluted sulphuric acid) as well as gel batteries and AGM batteries.
Lithium batteries have been tried and tested for use in small consumer appliances and power tools due to their high energy density and low weight. They are now also available as high-performance batteries based on lithium iron phosphate (LifePO4) and lithium nickel manganese cobalt oxide (LiNMC) technology.
Maintenance-free lead/acid wet batteries
The wet batteries available from us are maintenance-free. Thanks to their lead alloys and sealed housing designs with a pressure relief valve, the batteries have such low water loss that they carry enough acid for their entire life cycle. If excess gases are produced during operation or charging, these can escape through the valve via a small vent in the upper part of the housing. Maintenance-free marine wet batteries tolerate greater heels/slopes without acid leakage. Nevertheless, they should be placed in an acid-proof battery box and in a well-ventilated location. Our maintenance-free marine wet batteries can be used as starter/bow thruster and consumer batteries. To prevent premature battery wear, a discharge depth of ideally 35% to a maximum of 50% should be maintained. A deep discharge can lead to irreversible damage.
Gel batteries belong to the group of Valve Regulated Lead Acid (VRLA) batteries with a completely closed housing, in which the battery acid is thickened with kieselguhr. The gases produced during operation recombine to water inside the housing of the boat battery. Gel batteries are extremely low in gassing, leak-proof and can be used in boat or vehicle interiors regardless of position (but not overhead). There is no loss of capacity due to acid stratification/separation. The electrochemical processes in GEL batteries are not as efficient as in wet batteries, they have a higher internal resistance, with the advantage of very low self-discharge and very good storage capability. However, they are less suitable for providing high currents for short periods of time, for example to start the engine. Therefore they are ideal consumer batteries. The recommended discharge depth is 50%. Occasional deeper discharges are tolerated, but are at the expense of service life. A total deep discharge will also ruin a GEL battery.
AGM (Absorbent Glass Mat) is the most modern lead/acid boat battery variant, in which the battery acid is bound in a fiberglass mesh. Like gel batteries, they have a completely closed housing and are also valve-regulated, absolutely leak-proof and low-gassing, shock and vibration-resistant, can be mounted and operated in any position (except overhead) and have a low self-discharge rate. Compared to the GEL battery, the electrochemical processes in AGM batteries are much better. AGM has a lower internal resistance. This means that an AGM battery can absorb larger charging currents and also emit larger consumption currents. AGM can be used both as a consumer battery and starter or bow thruster battery. The recommended discharge depth is 50%. Occasional deeper discharges are tolerated, but are at the expense of service life. More than 80% discharge will cause irreversible damage. "Deep Cycle" AGM batteries are optimised in design and can be discharged regularly more than 50%, but never more than 80% (observe manufacturer's instructions!).
Due to their high energy density and low weight, lithium batteries have been tried and tested for use in small consumer appliances and power tools and are now also available as energy storage devices with large capacities. To achieve the required nominal voltage and capacity, these batteries consist of a large number of individual lithium cells, which are connected in series and in parallel to form larger cell blocks.
The Lithium Iron Phosphate (LiFePO4) and Lithium Nickel Manganese Cobalt Oxide (LiNMC) cell technology and a Battery Management System (BMS) used in the marine and automotive sectors ensure maximum performance and operational reliability. The BMS protects the battery against surge voltage and deep discharge as well as excessive charging and discharging currents. It monitors the battery temperature and controls cell balancing, i.e. ensuring that all cells in the battery are always at the same charge level. Depending on the manufacturer, additional functions are available via the BMS, such as integrated charge level display or Bluetooth battery monitoring.
Lithium batteries are far superior to lead acid types in many respects.
- They have a very high energy density and weigh only about half as much as lead-acid batteries with a comparable capacity.
- Depending on the BMS, 80-100% of the nominal capacity can be used instead of 35-50% for lead acid types.
- They provide a largely stable output voltage even at high loads.
- Even at low charge, lithium batteries can still supply their nominal current.
- Lithium batteries are fast charging and can be fully recharged within 1-2 hours.
- They can be used in a partially charged state without any problems and do not need to be regularly fully charged, as is required for lead acid types to maintain their performance.
There are a number of different lithium battery options for marine and automotive applications.
Thanks to integrated, high-performance battery management systems and the use of standard battery housings, it is now also possible to easily replace existing types of lead acid battery. These batteries are also known internationally as drop-in batteries. Drop-in batteries do not require additional external components such as safety relays or BMS.
The drop-in battery must be able to supply a high enough continuous and short-term (30 seconds) peak current for the powerful consumers on board.
Make sure that all charging technology on board meets the requirements of the lithium battery. Information on the charging voltage and charging current can be found in the operating instructions or in the battery data sheet.
Depending on the manufacturer and type, lithium batteries can be connected in parallel or in series to achieve greater capacities or higher system voltages. It is essential to observe the specifications of the battery manufacturer.
Niko F. on 29.03.2023
All was perfect.
Ulf Torbjörn J. on 29.03.2023
Ivo N. on 28.03.2023