This Lagoon 42 catamaran boasts a 1600 watt solar system that charges two RELiON RB-300 LT lithium batteries that power a Magnum 3000 watt inverter for running navigation equipment, lighting, three refrigerators, one freezer, a freshwater maker, a washer/dryer, a smart TV, plenty of cooking gadgets such as a rice maker, mixer and blender, an espresso maker, a coffee grinder, computers, and camera gear.
Many boaters are considering replacing lead acid batteries with Lithium Ion batteries. If you are considering making the switch to Lithium batteries, this article will hopefully answer questions you may have, so that you can make an informed choice. Topics covered include the safety, performance, charging requirements, cost, and common marine applications for Lithium Ion batteries.
The term Lithium Ion encompasses multiple chemistries having slightly different compositions. This results in variations of energy and power density, lifespan, cost, and safety. Common battery types are Lithium Cobalt Oxide (LCO), Lithium Manganese Oxide (LMO) and Lithium Iron Phosphate (LFP). Lithium Iron Phosphate is commonly considered the most stable, or safest of the Lithium-Ion chemistries. At West Marine, we view safety and reliability as the top priorities, which is why we recommend Lithium Iron Phosphate batteries for use on boats.
So, what makes Lithium Iron Phosphate batteries a viable option for boats? Below where the term “Lithium battery” is used, we are referring to the RELiON and Mastervolt branded Lithium Iron Phosphate (LFP) batteries sold by West Marine. We have summarized the key advantages that Lithium batteries hold over lead-acid, gel and AGM chemistries.
Key Advantages of Lithium Batteries
- More usable power
- Charge at a faster rate
- Increased cycle life for longevity
- Light weight for improved performance
- Built-in intelligence with a battery management system (BMS)
Lithium Batteries Deliver More Usable Power
RELiON lithium ion batteries installed on Lagoon 42 catamaran.
Lithium batteries operate at a consistent voltage through a majority of their discharge cycle. This difference means that Lithium batteries provide noticeably more power throughout a discharge cycle and do not respond with voltage “sag” when large loads are turned on. This helps to guarantee the dependable performance of electrical equipment and motors.
Lithium Batteries Charge at a Much Faster Rate
Lithium batteries are very efficient while charging due to their consistent or flatter voltage in the middle of the charging curve. Lithium Iron Phosphate battery chemistry allows fast charging with accepted charge currents as high as 50% or more of the battery’s amp hour rating. This means that with the right size charger, a full charge can be achieved in as little as two and a half hours. Finally, because Lithium batteries do not require a full charge after every use, they can be left in a partial state of charge without causing harm or shortened lifespan. These differences are summarized in the table below.
Table 1: Charging times of 100Ah Group 31 Lithium Iron Phosphate, Flooded Lead Acid and Gel/AGM Batteries*
| Charging Amps | Discharge Level | Lithium | Flooded LA | Gel, AGM |
|---|---|---|---|---|
| 10 | 0.5 | 5 hr. | 8 hr. | 8 hr. |
| 20 | 0.5 | 2.5 hr. | 4 hr. | 4 hr. |
| 50 | 0.5 | 1 hr. | Not feasible | Not feasible |
| 10 | 1 | 10 hr. | 16 hr. | 16 hr. |
| 20 | 1 | 5 hr. | 8 hr. | 8 hr. |
| 50 | 1 | 2.5 hr. | Not feasible | Not feasible |
Lithium batteries offer far greater cycle life.
A “cycle” is the combination of a discharge and recharge event that is over 5% of the battery’s amp-hour capacity. A standard flooded lead acid battery has a typical cycle life of 250 cycles. A high-performance AGM battery has a cycle life of around 500 cycles. For both a flooded lead acid and AGM battery those life cycles are based on up to 50% depth of discharge. If you discharge to 80% or more, you can reduce the cycle life by over 50% based on the frequency of discharge or age of the battery. In comparison, a Lithium Iron Phosphate battery has a typical cycle life of 3,500 cycles down to 80% depth of discharge. That is 3,000 more cycles than a high-performance AGM with 60% more usable energy.
Table 2: Cycle Life and Available Amp-hours Over Lifespan of 100Ah Group 31 Batteries
| Battery Type | Depth of Discharge | Cycle Life | Usable Ah Over Lifespan | % Versus Lithium |
|---|---|---|---|---|
| Flooded Lead Acid | 0.5 | 250 | 12,500 | 4% |
| High Performance AGM | 0.5 | 500 | 25,000 | 9% |
| Lithium Iron Phosphate | 0.8 | 3500 | 280,000 | 100% |
Lithium Batteries Weigh Less
Lithium batteries weigh much less than their lead acid counterparts. Because of this, serious sailboat racers, who are always looking to gain an edge by reducing the weight of their boats, are an obvious application for lithium batteries. Powerboat owners can benefit as well; since the reduced weight of lithium batteries results in better weight distribution and less draft, they can get on a plane faster with less fuel consumption.
Table 3: Weights of Group 31 Flooded and AGM Compared to RELiON R100 Lithium Battery
| Flooded Lead Acid | AGM | Lithium |
|---|---|---|
| 60 lb. | 69 lb. | 26.5 lb. |
Is the cost of Lithium batteries justified?
Bonita, Yoshi and their hound Marley enjoy an off-the-grid, solar powered lifestyle on their cutter-rigged sloop Nandji. According to Yoshi, the couple switched to dependable RELiON lithium batteries because, "Our lead acid batteries were simply not handling the constant strain we would put on them daily and they eventually died after just eighteen months."
Cost is often the first thing that comes to mind when it comes to lithium batteries. In a group 31 size a Lithium battery typically costs 7 times more than a traditional lead-acid battery, and 3 times more than a high-performance AGM. The higher cost has been the primary barrier against boaters adopting lithium batteries. However, the true cost of ownership is far less than lead-acid when considering life span and performance. Lithium typically has around 10 times the lifespan of a traditional lead acid and 7 times the lifespan of a high-performance AGM. If you assumed a battery on a boat was cycled once per day, then a flooded lead acid battery would typically last a year, a high-performance AGM would last a little over a year, and a Lithium would last nearly 10 years. Depending on the cost of your current batteries, the frequency, and the way you use your boat, Lithium can pay for itself in just a few years.
A Built-In Battery Management System (BMS) Protects Your Investment
RELiON Lithium batteries include an internal battery management system (BMS) that protects against harmful conditions before they occur. Think of this as the intelligence system that guards against users damaging their investment. A BMS makes sure each cell in the battery remains within safe limits. A well-designed battery management system can help maximize the lifetime and ensure the safe operation over a wide range of conditions. Conditions that the BMS protects against are over-voltage, under-voltage, over current, over-temperature and short circuit protection. When a BMS enters protection mode, the cell pack is electrically disconnected from the battery terminals and the battery voltage is no longer available. When the fault condition is removed the BMS will recover, and voltage is restored. We should mention that due to the protection the BMS provides against abuse or user error, RELiON (who warranties their batteries for 10 years) reports virtually zero returns. For more information about the BMS, please consult the applicable RELiON spec sheet or owner’s manual.
What type of battery charger do Lithium batteries require?
Yoshi shows off his RELiON lithium battery installation.
In standard conditions, Lithium batteries have a flatter voltage profile which allows the charger to provide maximum current longer resulting in faster charge times than lead-acid. For that reason, to maximize the potential of a lithium battery we recommend pairing it with a charger that has a designated Lithium charge profile. West Marine offers multiple chargers compatible with Lithium like the ProMariner ProNautic and ProSport HD battery chargers. Additionally, all Mastervolt battery chargers, DC to DC converter, and Inverter/Chargers are Lithium compatible.
When the BMS disconnects the battery, it disconnects it from the charging sources and the loads, so while the battery will be protected, disconnecting a battery from the entire electrical system could have other adverse effects.
Battery Monitoring
Since Lithium provides consistent voltages throughout the discharge cycle, voltage is no longer an accurate measure of state of charge. A traditional voltmeter that provided insight into the level of charge in a lead-acid battery will not be effective for monitoring lithium batteries. The only way to measure the state of charge of lithium is with a State of Charge (SoC) monitor. We recommend SoC meters with shunts that monitor all the amperage flowing in and out of the battery. West Marine offers multiple SoC meters like the Blue Sea Systems M2 DC Multimeter with SoC.
What Size Lithium Batteries Do You Need?
As discussed earlier one of the primary benefits of Lithium batteries is the ability to deeply discharge vs lead-acid. When selecting the proper amp hour size or quantity of lithium batteries we still recommend creating an energy budget as outlined in the West Advisor Article Sizing Your House Battery Bank. The only difference is when creating an energy budget with Lithium you don’t have to be concerned with restricting your depth of discharge to 50%. For example, if your energy budget per day is 120Ah with lead-acid we recommend a 3-4 multiple resulting in a battery bank 360-480Ah. With Lithium the Ah per day multiple can be 1.5-2, or in this example 180-240Ah. For most boaters this will allow the use of less and/or smaller Lithium batteries in a boat that previously used lead-acid.
Just like with lead-acid batteries, connecting Lithium batteries in parallel to increase capacity is acceptable. For example, wired in parallel 3X 100Ah batteries will result in a 300Ah bank. However, it is recommended to consult your battery’s owner’s manual for designing battery banks of five or more batteries.
Charging Lithium Batteries with an Alternator
Patrick Walters, Elite Series Pro Angler installing a RELiON lithium battery. Tournament bass anglers appreciate the performance and reliability of RELiON lithium batteries which enable them to fish longer before they need to recharge.
Lithium batteries have been in wide marine use and successfully charged by alternators for several years now. Like with standard AC battery chargers it is critical to ensure your alternator/regulator is compatible with Lithium. Anytime the battery’s BMS determines charging in unsafe levels it will disconnect the battery from the system. With AC charging this is not a major issue, but with alternator charging that could mean your alternator is running with no battery present which could back feed and damage components. For that reason, we recommend only pairing lithium batteries with alternators and regulators with designated lithium profiles. West Marine offers multiple external regulators from Balmar and Mastervolt that work with lithium.
A recommended alternative to changing out an alternator is to install a DC-to-DC converter. These devices allow you to leave the alternator connected to the existing lead-acid battery bank. The DC-to-DC converter then connects the lead acid bank to the lithium bank and appropriately isolates, and properly charges, the lithium bank using the existing alternator. West Marine offers multiple DC-to-DC converters in various sizes and styles from Mastervolt.
Engine Starting
While the characteristics of Lithium batteries make them ideal for house power applications, most lithium batteries are not designed for engine starting. The typical peak current on a standard RELiON battery is 200A and it should not be used for engine starting. Fortunately, West Marine does offer the HP line of batteries from RELiON that has a peak current of 800A for two seconds. This is one of the only Lithium batteries designed and rated for engine starting in the industry. Like other Lithium batteries, the RELiON HP series is also a deep cycle battery making it a true dual-purpose option.
Connecting Lithium Batteries in Series
Series connections may also be needed when sizing a battery bank for the correct voltage. For example, boaters will often connect 3 x 12V Lithium batteries in series to power a 36V trolling motor. One must be selective though as not all Lithium battery models are designed to be wired in series. The series capability is listed on all RELiON battery specification sheets. For example, the RB100 battery allows for connecting up to six 12V batteries in series for a total of 72 volts. Keep in mind, the best way to charge a battery bank connected in series, is to use a charger that has a dedicated charging lead to each bank like the ProSport HD line of battery chargers.
One of the additional benefits of lithium is the availability of batteries at a nominal voltage above 12V. West Marine offers multiple 24V lithium batteries. This enables 24V customers to simply purchase one battery to achieve their system voltage and then connect them in parallel if more capacity is desired.
Can Lithium batteries benefit you?
Patrick Walters, Elite Series Pro Angler next to his RELiON battery installation.
How you use your boat will be one of the largest factors in determining if Lithium makes sense. We have found that boaters with heavy electrical load requirements are the ideal candidates for a Lithium battery system.
Examples of Lithium Battery Applications
- Trolling motor batteries because Lithium allows the angler to fish longer
- Cruisers who want to travel further and stay at a destination longer
- Boats with large power devices like stereo amplifiers, gyros, and air conditioners
- Generator alternative. The combination of an Inverter Charger and appropriately sized Lithium battery bank replaces the noise, hassle, and maintenance of a generator while giving the boater the same comforts of home
While Lithium may not be right for all boat applications, we hope this article has given you information to consider if Lithium is right for your next battery replacement.