Marine Lithium Batteries For Boats
How a live-aboard sailing couple upgraded to LiFePo4 lithium batteries for enhanced safety and efficiency.
We’ve been full-time live aboard sailors for the past 15 years, so having a safe, reliable, and efficient battery bank that can keep up with our power demands has always been a priority. Like many boaters we started out with standard lead acid batteries designed for the auto industry. We weren’t long off the dock before finding them lacking. A few years later we upgraded to a brand of deep cycle lead acid batteries popularly used in golf carts.
Immediately, we noticed that our solar panels seemed more efficient, which was really just the batteries being able to store more energy for longer. This freed us from having to top up via the engines alternator every few weeks. When we switched to AGM’s designed to work primarily with solar applications, we were surprised at the increased stamina of our new batteries. As AGM’s are completely sealed, we happily also noticed that there was no longer a sour smell in the battery compartment. However, after eight years there was a marked decrease in performance. It was time to reassess our battery situation.
Switching to lithium batteries for our house bank is something that we’ve been thinking about for years. However, haunted by stories of overheating batteries and vessels being destroyed by fire, not to mention the hefty price tag, the cons outweighed the pros. That is until recently. Thanks to developments in composition and manufacturing, lithium batteries are now safer and available at competitive prices. Six months ago we took the leap into lithium and installed a pair of LiFePo4 batteries. The learning curve has been steep, but very rewarding.
Difference In Lithium Batteries
Everyone who owns a cell phone, laptop, fitness tracker, or any other rechargeable gadget has experience with Li-Ion, or lithium ion, batteries. They are efficient, incredibly energy dense, and very economical. However, if you’ve ever left your device on the charge for longer than necessary, or used the high current fast charge mode, you know that Li-ion have a habit of getting very, very hot.
Above: Lithium-ion batteries offer a huge weight savings over traditional lead-acid batteries. Image via Ed Sherman.
This overheating can lead to thermal runaway in Li-ion batteries, which is the greatest safety concern. Thermal runaway causes violent spontaneous explosions and intense fires which are difficult to extinguish. Thermal runaway can occur when a Li-Ion battery is damaged due to being dropped or punctured, if it has an internal short – often due to poor manufacturing standards, if it gets wet, overheated, or over charged.
Lithium Ion Batteries Fire Hazard Issues
The New York Fire Department reported that 18 people died due to Li-Ion battery fires in 2023. An increase of 300% over the previous year. In a recent statement, the National Transport Safety Board said that a fire that caused $3 million dollars in damage to an oil tanker anchored off Louisiana in November 2022 was caused by the thermal runaway and explosion of a handheld radio’s Li-ion battery. If small Li-Ion batteries can cause that much damage it is no wonder people have been reticent to swap over to Li-Ion for larger applications.
LiFePo4 batteries still contain lithium but thanks to the variations of the other chemical compounds they are not nearly as combustible. LiFePo4, or Lithium Iron Phosphate, batteries are often credited as the safest lithium batteries on the market due to the improved thermal properties. They have a greater range of working temperatures, and they don’t heat up as easily when in use or charging. Most importantly, LiFePo batteries are not prone to thermal runaway. They don’t explode if punctured or damaged.
The nominal charge of a LiFePo battery is about 3.2 volts, which slightly lower than the nominal charge of a Li-Ion. At first glance this is not an earthshattering difference, however it does equate to a LiFePo’s being slightly more compatible with 12V systems. This in combination with the stability of the battery is why the heavy industry uses LiFePo batteries to power equipment like diggers and backhoes, why there is a surge in the EV market for LiFePo batteries, and why more and more boaters are making the switch.
Longer Battery Life-Expectancy
Perhaps the biggest selling points for the LiFePo batteries is that they have a deeper degree of discharge and longer life expectancy. Unlike many other kinds of batteries, LiFePo batteries can be fully discharged without compromising future charge capacity. This lack of charge memory is real bonus when it comes to powering vehicles or boats. LiFePo batteries also have more discharge cycles than Li-Ion batteries. On average 2-4 times more. This means LiFePo batteries could give 10 years of efficient service.
The safety aspect of these batteries is a huge advantage, but there are draw backs to any technology. LiFePo are not as energy dense as Li-ion batteries. This means that in a side-by-side comparison between the two, a LiFePo battery will have a slightly larger footprint than a Li-Ion battery of the same capacity. The size difference is nominal but in applications where you want to get the most bang for your buck, important. Lastly, the initial expense of LiFePo batteries tend to be 20-25% more than Li-Ion. However, take into account the extended battery life and efficiency, and they end up being the cheaper battery in the long run.
LiFePo AND THE BMS
All LiFePo batteries should come with a BMS, or Battery Monitoring System. This small electronic component is the brains of the battery. Usually Bluetooth compatible and housed inside the battery casing, the BMS allows the user to interface with the battery to monitor overall charge and discharge rate, individual cell charge rate, and battery temperature. The BMS is also where settings for temperature and charge/discharge cut offs are found. The BMS is not a charge controller, as is found in a solar set-up, but rather a way to communicate with the battery. It acts as a safety net, allowing for somewhat customizable battery set-up.
LiFePo4 On Board
The initial install of our LiFePo4 batteries was easy. That they weigh 50% less than a lead acid of the same size made hauling them on board almost pleasurable. We ordered batteries that have a similar footprint to our previous AGM’s, so they fit nicely into our battery compartment. Equipped with standard battery posts, there was no need to change any wiring. It was as close to plug-and-play as a boat project can get.
It was necessary to change the parameters on our solar charge controller since LiFePo batteries have a different charge algorithm. Most newer systems will have built in lithium parameters to select. We ended up having to upgrade our shore power charger because our current model wasn’t lithium battery compatible. We also bought a DC to DC charger to act as a interpreter between the alternator and the batteries, allowing us more efficient charging while motoring.
It took a couple weeks to get used to, and if I am honest trust, our new batteries. While the BMS displayed all the correct information, it was a matter of learning to translate that new information to fully understand how the batteries were charging/discharging. We tested the auto cut off settings, tinkered with the solar charge controller settings, and did a bulk charge using our new shore power charger.
Conclusion
What has made the biggest impact in our everyday routines is that there is no longer any need to worry about whether the battery charge dips too low over night. 50% charge was the cut off point to keep our AGM’s at peak performance. If we had a string of cloudy days we would often have to sit listening to the engine or opt to turn off our fridge at night. Since the LiFePo4 batteries don’t have a charge/discharge memory we haven’t had to do either since we’ve installed them. The fridge is working better and the beer is colder. The crew is happy with our investment.
