Frequently Asked Questions about Batteries
The battery as power source
There are different kinds of rechargeable batteries. The most common type is the lead-acid battery. A less familiar one is the nickel-cadmium (NiCad) battery, which can still often be found in old emergency power systems. Due to the high charge voltage required by a NiCad battery, and the fact that they are very environmentally unfriendly, these batteries are not suitable for use onboard a vessel or car/truck.
The starter battery
A starter battery has many thin plates per cell, leading to a large total plate surface. This type of battery is, therefore, suitable for delivering a high level of current over a short period of time. The number of times that a starter battery can be heavily discharged is limited to around 50-80. But as starting the engine uses only a small part of the energy stored (around 0.01 %), the battery lasts for many years. This type of battery is generally unsuitable for cyclic use.
The semi-traction
A semi-traction battery has fewer but thicker plates in each cell. These batteries supply a relatively lower starter current, but can be discharged more often and to a greater extent (200 to 600 full cycles). This kind of battery is highly appropriate for the combined function of starter and service battery.
Which battery is suitable for my application?
Η Mastervolt offers various types of maintenance-free batteries, each with its own specific characteristics. More information hereafter about the properties of gel, AGM and Lithium Ion batteries.
With flooded lead-acid batteries, which use a liquid electrolyte of water and sulphuric acid, the water is separated into hydrogen and oxygen during charging, mostly at the end of the charging cycle. These gases subsequently escape through the filler cap. This means water is used and distilled (battery) water needs to be added. The electrolyte in a Gel battery is a gel that binds the water with the acid.
While the batteries are being filled, the gel is heated and liquefies.After the battery has been filled with the liquefied gel, the gel cools and solidifies. This process results in tiny hairline cracks in the gel between the plates. During the charging process, oxygen O2 is generated on the positive plate and hydrogen H2 on the negative plate. The cracks in the gel let the gases combine to create water. The gel then absorbs the water so that no water disappears from the system and no gases are produced.
Gel batteries are not a new technology and have been in use since the late 1950s. The most important applications are in emergency power systems, telecommunications systems, power supply and, for the last 20-25 years, as service batteries in various systems.
Gel batteries come in two different versions.
- The 12-volt design is appropriate for regular use and available in capacities up to 200 Ah.
- The second design is a 2-volt traction battery, available in capacities up to 2700 Ah and highly suitable for systems with frequent and significant discharging where a long lifespan is needed.
For a battery of 12 or 24 volt, six or twelve Gel batteries need to be connected in series to provide the required voltage.
Major benefits of Gel batteries include very limited self-discharging, the possibility of a short charging time, and the lack of gas production under normal circumstances. All of this makes Gel batteries very suitable for heavy cyclical applications.
A different type of lead-acid battery is the AGM (Absorbed Glass Mat) battery. In this model, the electrolyte (water and sulphuric acid) is absorbed into an extremely delicate glass fibre mat. Just like with any other battery, charging generates hydrogen gas and oxygen, which are transported through the capillary tubes of the glass fibre mat. Once the two gases are recombined, water is once again obtained and subsequently reabsorbed into the glass fibre mat. The recombination process is then complete.
The glass fibre mat also serves as insulation between the plates, allowing the plates to be close together and leading to very low internal resistance. This means that a high discharge current is no problem. The charge current could be a little lower than with Gel batteries (approx. 30 %) because the glass fibre mat is also an efficient heat insulator, and heat generated by charging is gradually conducted to the outside of the case. This requires the charge current to be somewhat restricted and results in a slightly longer charging time.
AGM batteries are highly suitable for applications requiring a high discharge current, such as a bowthruster or winches and for medium cycle use. The AGM battery is entirely closed and therefore maintenance-free. If the AGM battery is overcharged, for instance due to the use of a (cheap) unregulated battery charger, a small amount of hydrogen gas is formed. This gas escapes through a special vent in the battery casing that is designed to prevent oxygen from entering the battery. Incorrect charging will reduce the battery’s lifespan.
Until recently, Lithium Ion batteries were mainly available as chargeable batteries with a small capacity, which made them popular for use in mobile phones and laptops. Mastervolt offers Lithium Ion batteries with large capacities. Our Lithium Ion batteries have a high energy density and are perfect for cyclic applications. Compared to traditional lead-acid batteries, Lithium Ion batteries offer savings of up to 70 % in volume and weight, while the number of charging cycles is three times higher than semi-traction lead-acid batteries. An added benefit is that Lithium Ion batteries can supply a constant capacity, regardless of the connected load. The available capacity of a lead-acid battery is reduced in case of higher discharge currents. Lithium Ion batteries can be discharged to 80 % without affecting their lifespan, whereas lead-acid batteries are more affected by deep discharge. Compared to traditional open or lead acid batteries, the Lithium Ion batteries offer even more benefits, such as a much larger power density and a longer lifespan. And because lithium is the lightest metal, Lithium Ion batteries are also more lightweight. They can also be charged at any time, while nickel-cadmium batteries require complete discharge for an optimal performance and to prevent memory effect. Furthermore, Lithium Ion batteries can be charged with a very high current, up to 100 % of the capacity, resulting in a very short charging time and no memory effect. Mastervolt Lithium Ion batteries are equipped with a Battery Management System. The system keeps all the individual cells perfectly balanced, resulting in a higher capacity and longer lifespan.
Mastervolt's Lithium Ion batteries are based on Lithium Ion iron phosphate, which has an energy density three times higher than that of lead-acid batteries. Although there are materials with an even higher energy density, these are generally considered less safe. The Mastervolt Lithium Ion batteries are therefore considered one of the safest batteries of their type. A unique feature is their built-in Battery Management System (BMS). The system monitors the cells and guarantees optimal safety. Mastervolt Lithium Ion batteries are MasterBus compatible, and up to 15 % more efficient compared to other Li-ion batteries available.
This gives you:
- Shorter charging times.
- Less generator time required for charging.
- More power than from a traditional battery of the same dimensions. A normal open lead-acid battery, for example, has a DOD (depth of discharge) of 50 %. This means that you can only use up to 200 Ah from a 400 Ah battery. A Mastervolt Lithium Ion has a DOD of 80 %, almost 60 % more usable battery capacity. With this percentage, a battery of 400 Ah supplies 320 Ah, or 120 Ah more.
- MLI batteries are ideally suited for electric and hybrid propulsion, and can be connected unlimited in parallel or up to ten units in series (series connection is not possible for the MLI-E model).
- MLS batteries are not suitable for series connection, but can be configured unlimited in parallel (see manual for more information).
- Another benefit is that Lithium Ion batteries weigh less and require less space.
Determining the lifespan of a battery
The lifespan of a battery will vary considerably with how it is used, how it is maintained and charged, the temperature and other factors. Also the type of battery will determine its lifespan.
12 Volt Gel or AGM batteries
If kept in a charged state when unused, the common lifespan of a 12-volt Gel or AGM battery is up to six years. After five or six years of float voltage at an average ambient temperature of 25 ºC, the battery still retains 80 % of its original capacity. Higher average temperatures will shorten the lifespan of the battery. The number of charge and discharge cycles of a 12-volt battery is strongly correlated to its structure and quality. Mastervolt’s 12-volt Gel batteries can take around 500 full cycles of being discharged down to 20 % and charged back to full capacity. Most manufacturers consider batteries to be spent at a remaining capacity of 80 %. This does not, however, mean that the battery has to be replaced immediately. For example, the battery can still be used if only 50 % of the battery capacity is actually required. It is therefore not necessary to replace the battery after six years or 500 full cycles. An average use of seven years is perfectly normal for 12-volt Gel or AGM batteries..
2-volt traction Gel batteries
The lifespan for 2-volt traction Gel cells is at least 15 years and the maximum number of full cycles is 1000-1500 when discharging to 20 % of capacity. These batteries are therefore highly suitable for larger systems that require intensive use and a very long lifespan.
Lithium Ion batteries
Mastervolt Lithium Ion batteries have a lifespan of more than 2000 cycles, which is three times longer than most standard lead-acid batteries. They have an extremely long lifespan due to aspects such as the battery management, very low self-discharge, the lack of memory effect and a discharge of up 20 %.
Conclusions and recommendations
AGM batteries
The low internal resistance of AGM batteries makes them highly suitable for powering winches, windlasses and bowthrusters, for starting engines, and for limited cyclic use.
Gel batteries
Gel batteries are highly suitable as service batteries due to the fact that they can be quickly charged and have a long lifespan, even with many charge/discharge cycles. For a service battery you can choose for either a 6-volt, 12-volt or 24-volt version or the 2-volt model.
Lithium Ion batteries
Lithium Ion batteries save up to 70 % in space and weight, last three times longer and can be recharged and discharged very quickly, 2000 charge cycles in normal use.
Mastervolt batteries are completely maintenance-free and in normal circumstances do not release acid or generate dangerous gas. They are easy to install anywhere onboard, such as next to the bilge or in the engine room (the latter may lead to reduced lifespan due to higher temperatures). Special battery cases or external ventilation are usually unnecessary as natural ventilation will suffice.
Frequently Asked Questions about Batteries
How long will it take before my battery is discharged?
This depends on its capacity and the amount of power consumed by the connected equipment. As a rule, the faster a battery is discharged, the less power it supplies. This also works the other way around: The longer it takes before a battery discharges, the more energy you can get from it.
A 100 Ah lead-acid battery supplies a current of 5 amps for 20 hours, during which time the voltage does not drop below 10.5 volt. This amounts to 100 Ah. If a load of 100 amps is connected to the same battery, the battery will be able to power it for only 45 minutes. After this time the battery voltage will fall to 10.5 volt and the battery will be empty, having supplied no more than 75 Ah. In contradiction to the lead-acid batteries, the capacity of Lithium Ion batteries will not be effected by the load connected. A Li-ion battery will always supply 100 % capacity, independent of the connected load.
How long will my battery last?
The lifespan of a battery is related to how often and to what extent it is discharged. Proper charging with the right charger is also crucial. At a normal use for holidays and weekends, a lifespan of between five and seven years is quite common for Gel and AGM batteries. When batteries are frequently discharged you will need to adjust the capacity. There is also an option to use 2 volt cells. A lifespan of 15 years is not exceptional for this type of battery as long as they have the right capacity and are properly charged. Lithium Ion batteries are top of the bill. You can discharge and recharge them super-fast and they last up to three times as many cycles than other types of batteries.
What not to do with Gel, AGM and Lithium Ion batteries?
- Incorrect charge voltage. Too low a voltage means that the battery cannot charge to 100 % - the sulphate then hardens on the plates and the battery loses its capacity. Excessive voltage causes the batteries to generate gas, leading to water loss and drying out.
- Excessive discharging. Discharging a battery further than its capacity shortens its lifespan.
- Too large ripple on the charge voltage.Cheap and old-fashioned chargers often have a significant voltage ripple (voltage variation) in the output voltage.
- The use of an alternator without 3-step regulator, a high ambient temperature or charging without temperature compensation. The MLI battery should not be charged without measures such as a safety relay.
Can I keep my batteries connected during winter?
This is no problem for any Mastervolt battery, and can even be a benefit as the lower temperature extends battery life considerably. The batteries should be fully charged, however, and disconnected from any consumers. Make sure to consider hidden consumers such as voltmeters, clocks and the car radio memory. If the battery is connected to a Mastervolt battery charger with 3-stage+ charge characteristic, the battery is recharged every 12 days to ensure it stays in optimal condition. If you disconnect the battery we recommend disconnecting all consumers and connecting the power once every two to three weeks to ensure the batteries are recharged. If you don’t have access to power in winter, we recommend fully charging the batteries and disconnecting the battery terminals to ensure they are not discharged by small devices. We also recommend fully charging your batteries every two months and before they are reused. Wet batteries should be recharged regularly to prevent them from freezing.
How should I maintain gel, AGM and Lithium Ion batteries?
Gel, AGM and Lithium Ion batteries as opposed to traditional open batteries do not need maintenance, which means they can be installed anywhere. However, we recommend checking all the connections once a year to make sure that they are properly attached, and to clean the top surfaces with a slightly moist cloth. The batteries also need to be completely charged every time for a maximum lifespan.