Lithium
Deep Cycle Marine Battery Basics
The lithium deep cycle marine battery is making rapid inroads into boat electrical power systems. Lithium-ion batteries use lithium cobalt dioxide (LiCoO2) or lithium manganese oxide (LiMn2O4) as a cathode. A lithium-iron battery uses lithium (Li), iron (Fe), phosphate (PO4), or LiFePO4, as the cathode and these are the most common on boats. Lithium-ion batteries using lithium cobalt dioxide are common in electric vehicles, solar power systems and portable devices. LiFePO4 batteries are broadly considered as safe to use and safety risk are associated with damage or high temperatures.
Like most battery technologies, the battery cell comprises two electrodes which are the cathode and anode, with an insulative separator or barrier between them. The anode stores the lithium and is made from graphite carbon with a metallic backing. The cathode stores lithium and is manufactured with a metal oxide chemical compound (LiFePO4).
Lithium
Deep Cycle Marine Battery
The ABYC published revised lithium-ion battery recommendations in chapter E-13 in 2023. In 2022 the United States Coast Guard (USCG) requested that the ABYC test Lithium Iron Phosphate (LiFePO4) batteries and to try to replicate many of the reported issues and failures. They were unable to re-create any failures, regardless of how aggressive the testing was and have reportedly stated that lithium-ion batteries are safe. Following several major incidents, the jury is still out within the commercial maritime space. Lithium Ion Batteries for Boat has many elements. Portable device lithium batteries are the most common cause of fires, find out more here and also a bit more here.
Lithium
Deep Cycle Marine Battery Basics
The electrolyte has a key role within the lithium-ion battery cell, transporting positive lithium ions between the cell cathode and anode. The electrolyte used within lithium battery technologies comprises a very high purity lithium salt, which is lithium hexafluorophosphate (LiPF6). This white crystalline powder is dissolved within an organic carbonate solvent, or nonaqueous solution. Several other chemical additives are used in the electrolyte to attain the required electrolyte properties.
Lithium Deep Cycle Marine Battery Discharge
How much power can be delivered throughout the discharge cycle is the key to power supply quality and reliability. It should be noted that batteries can be damaged when over discharged. This is usually a result of cumulative small residual or parasitic loads, such as devices that run all the time. Contrary to popular belief these batteries should not be discharged 100% as they will be damaged and the life reduced. There is much more about batteries in the latest 4th Edition of my book The Marine Electrical and Electronics Bible.
Lithium
Deep Cycle Marine Battery Charging
The lithium ions pass through the cell separator and block the passage of the electrons. In the charging cycle, the ions pass from positive to negative; conversely, in the discharge cycle, they move from negative to positive. This movement of ions creates a potential difference and what we know as voltage. Lithium-ion batteries have a nominal voltage of 3.7vpc. Like other battery types, cells are connected in series to achieve the required battery bank voltage. That means four cells for a 14.8V battery. The cells are placed in parallel to increase the amp-hour capacity required. These batteries have a capacity rating of 1C, which means that a fully charged battery with a nominal capacity of 100A can discharge 100A in 1 hour, or 10Ah is 10A in 1 hour. Maximum discharge rates are usually rated at 2C. Like all batteries, regular charging and discharging is the best path to reliability. The average cell voltage across the discharge range is 3.6V to 3.7V; full charge is 4.2vpc, 3V when at minimum level. Running them down to 2.5vpc will damage them. A fully charged LiFePO4 battery will have a stable voltage of 13.3V to 13.4V; the lead-acid battery will be around 12.6V. It is important to note that undercharging by just small percentages can significantly reduce battery capacity. Find out more here.
Lithium Deep Cycle Marine Battery Charging
However, there are caveats with respect to charging. Unlike lead acid battery charging which has 3 stages lithium-ion batteries have just 2 which are the constant current (CC) phase and the constant voltage (CV) phase. LiFeP04 batteries need to be charged in the range 3.5V to 3.65volts per cell at least once every month to allow the BMS to rebalance the cells. They should be charged at constant current until the current level falls to 0.03C to 0.05C (check the battery manufacturers specifications) when the charging should stop to avoid cell overcharging. Most batteries have a charge current acceptance rate of around 50% of the battery capacity. A 150Ah battery is able to accept a constant 75A charge current. Alternators will require upgrading and a smart regulator such as the Wakespeed WS500 or the Balmar MC-614-H, along with others. As a standard alternator will literally supply full output to a battery until nearly fully charged they are quickly overheated and destroyed. More great information is here.
Lithium Deep Cycle Marine Battery
Lithium-ion batteries are intolerant to temperatures exceeding 140°F (60°C) and should always be stored in a cool place. The nominal range is -4°F to 140°F (-20°C to 60°C); storage at temperatures below 68°F (20°C) can result in permanent capacity loss. If you are laying up your boat, which is common through many US and European winters or in countries that experience subzero or reduced temperatures well below 68°F (20°C), it would be advisable to take the batteries out and store them somewhere at the house.
There are State of Charge (SOC) and voltage advisories as well for Lithium-ion batteries. Short-term storage is recommended in the range of 3.0V to 4.2vpc in series. For long-term winter layups, this is at about 7% to 80% of battery capacity or less with a voltage level of 3.85V to 4.0V. The battery will lose storage capacity if it is maintained at 100%. They do not like being run down below the minimum voltage, which is between 2.4V and 3.0vpc.
Lithium
Deep Cycle Marine Battery BMS
This is one of the reasons that a Battery Management System (BMS) should be installed at all times. Many quality batteries should incorporate this at cell level. The BMS monitors and shuts off when it detects either high or low voltage limits, high and low temperature limit and lastly when current charge limits are exceeded, both charging and discharging. The BMS should monitor these parameters at cell level. Only install batteries that are from reputable manufacturers with cell level BMS monitoring systems installed. There are equipment manufacturers that specify only selected Lithium-ion battery makes and models. Andersen compact deck winches are one of them. They only accept Super B, Mastervolt and Victron Energy (MG Energy Systems) batteries. These batteries have undergone compatibility testing and have integral protection to prevent battery, motor and systems damage. Lithium batteries are worth consideration.