Going Lithium

Marine lithium battery systems have undergone a remarkable evolution in recent years. If you’re looking to expand the battery capacity for your growing electrical needs, want to reduce long-term operating costs or reduce weight aboard your boat, a lithium battery installation may be in order.

Lithium Ion is a broad term that encompasses various lithium battery chemistries, but the dominant choice in the marine sector today is Lithium Iron Phosphate, commonly known as LiFePO4 or LFP. This chemistry mix has gained popularity for its safety features, long-term cost effectiveness, and extended cycle life. In terms of safety, a properly designed lithium system can be as safe or safer than a lead acid system.

Lithium battery conversion is an extensive topic that often leaves boat owners unsure of where to even start. First, we’ll focus on the advantages of lithium over lead acid and then compare and contrast internal and external lithium battery management systems (BMS). In a future issue, we’ll focus on how to design and install a lithium system.

Why Lithium batteries?

Although reliable and generally safe, lead acid batteries have many drawbacks when compared to lithium battery systems. Although lead acid battery technology has improved over the last 165 years, lithium’s entry into the marine market has been critical to meeting the electrical demands of modern-day boaters. 

For starters, lithium batteries offer significant capacity and lifespan advantages over lead acid batteries. A typical recommended depth of discharge (DoD) for a lithium battery is 80 percent with a lifespan of up to 4000 cycles. In comparison, lead acid batteries have a maximum DoD of 50 percent and 1200 cycles. Putting overall performance aside, despite their higher initial cost, lithium’s advantage in lifespan can make them cheaper than lead acid batteries over the long run.

Although lead acid batteries still make up the bulk of the market, they have significant disadvantages. While lithium batteries can be kept at reduced levels of charge without damage, lead acid batteries are prone to sulfation, a detrimental process that impacts battery lifespan and diminishes overall capacity. Additionally, lead acid batteries have a lower charge acceptance rate than lithium, which makes the use of high output alternators, large solar systems, and battery chargers significantly less effective as these batteries get closer to their full capacity.

But before you switch to lithium batteries, you should consult with your insurance provider to verify that they will continue coverage if you retrofit your boat. Many insurers will allow it, but they may require proof of professional installation to mitigate some of the risks of lithium batteries. Safety is also why battery management systems are important to lithium batteries.

So, what is a BMS?

A battery management system (BMS) plays a pivotal role in ensuring a lithium battery’s safety and performance. It serves as the primary safeguard against extreme temperatures, overcharging, and over discharging that could cause damage. Lithium batteries are commonly produced in two variations, either with an internal BMS configuration or an external BMS configuration.

While each offers distinct benefits, it’s important to understand the difference before you decide to convert your boat to lithium.

Internal BMS Batteries

Internal BMS batteries have emerged as a popular option as the marine industry continually transitions towards lithium battery technology. Often marketed as convenient “drop-in replacements” for lead acid counterparts, these internal BMS batteries are subject to standard lithium battery requirements, which is why it’s important to understand the full scope of their capabilities and limitations.

The internal BMS batteries are usually chosen for their ease of installation, which eliminates the complexity of the charging controls that are required for an external BMS system. Because each internal battery has its own BMS built in, it has one critical advantage over external BMS systems. If an individual battery fails, a properly configured setup with positive and negative bus bars will prevent the failed battery from disrupting the entire lithium bank. This ensures operational continuity, which may not always be the case with an external BMS system.

Unfortunately for internal BMS batteries, this reduced complexity comes with a downside in replacement cost. If a BMS or a cell fails it will necessitate the replacement of the entire battery, including its BMS, which can be more costly than with an external BMS system where you can replace just the broken cell or just the broken BMS.

Many internal BMS batteries do not allow for external communication with charging sources or system monitors. Alternator charging sources should be closely protected from a battery becoming disconnected by an internal BMS alarm that is not being communicated.

Not only could such a situation cause the alternator to fail, but it could also cause a large voltage spike that might harm sensitive navigation electronics. Lack of communication might also make it challenging to comply with ABYC E-13 standards to install a warning system. 

Lastly, internal BMS batteries are often significantly limited in their ability to be wired in series or parallel, preventing their use on large-capacity house banks and with voltages higher than their rated value. These restrictions are brand dependent, so it is important to reach out to the manufacturer before making a purchase.

Having said all that, internal BMS lithium battery technology is evolving rapidly, and these disadvantages are being addressed by many of the leading manufacturers. If you’re thinking of going with an internal BMS battery system companies like Battleborn, Dakota Lithium, Epoch, Abyss, Relion and Xantrex are worth checking out.

External BMS Batteries

External BMS batteries present a compelling alternative. Although they are more complex, they offer more versatility, a more diverse range of power and usage requirements, and provide boaters with greater control over their battery systems.

For one, external BMS batteries enable the BMS to independently regulate the charge and load sides. In case of an overcharging situation, the BMS can disconnect the charging side without disrupting the boat’s loads, ensuring uninterrupted operational integrity. Conversely, in case of an over-discharge, the BMS can isolate the load side while maintaining the charging side connection.

Compared to internal BMS battery systems, external BMS batteries are generally more cost effective to repair in the event of a component failure. External batteries also tend to have more flexibility when it comes to wiring, which allows for building larger Amp-hour (AH) banks or higher voltage configurations for larger boats and electric propulsion banks, provided that the manufacturer’s specifications are meticulously followed.

However, external BMS batteries do have their drawbacks. For one, they require that careful attention be given to the external wiring of the BMS, which can be more complicated. Charging and load controls and associated wiring all necessitate a greater degree of expertise and planning to the point where a detailed design drawing may be required.

Cost can be another drawback. While the individual batteries for an external BMS installation may come at a lower cost than an internal one, the total external BMS installation may be more expensive due to the additional wiring, control systems and labor requirements.

If you’re considering an external BMS lithium battery installation, Victron Energy, MG Energy Systems, Mastervolt and Lithionics are worth a look.

So, which battery configuration is right for you?

As a marine professional, historically I’ve leaned towards external BMS lithium systems for their flexibility in meeting the unique power requirements of each individual customer. However, as more internal BMS manufacturers embrace standardized communication protocols, incorporate Bluetooth-enabled cell and alarm monitoring features, increase charge and discharge capabilities, and decrease overall prices, the internal BMS lithium battery is emerging as a compelling choice.

A case can be made for either system, but it’s important to understand what your requirements will be before you move on to the next step: system design and layout.

This article was originally published in the August 2024 issue.