This year we replaced our lead acid batteries with LiFePO4 (Lithium Iron Phosphate) batteries. We wanted to learn how this technology functioned in a marine cruising environment and analyze how this technology operated with our solar system.
Battery Configuration - After considerable research, we selected a 100 Amp Hour (Ah) battery manufactured to our specification with a 150 amp draw Battery Management System (BMS) and Bluetooth capability. We worked closely with our manufacturer to design the best battery for the marine environment. We replaced our house bank of three 110 Ah lead acid batteries with two 100 Ah LiFePo4 batteries and replaced our 110 Ah lead acid start battery with a single 100 Ah LiFePo4 battery. We have three charging systems onboard; a 75 amp Balmar alternator with smart regulator, a Xantrex 55 amp inverter/charger for shore power and a 175 watt solar system with an EP Xtra-N Li capable solar controller. We have a Link 2000 battery monitoring system. We were able to replace our three battery house bank with two LiFePo4 batteries because the LiFePo4 batteries can be safely discharged 90% (180 Ah) whereas the lead acid can be safely discharged only 50% (165 Ah).
Findings Summary - These batteries performed beyond our expectations. They took everything we could throw at them through heavy charging and discharging. They proved to be plug compatible with our existing charging systems and compatible with our onboard appliances. The only disadvantage we could come up with is the cost but this is mitigated by the life expectancy of these batteries. We will keep these batteries onboard for a long time. Below are some specifics on our observations.
Bluetooth - The Bluetooth capability enables real time monitoring of each battery through an app on a smartphone. The system displays the state of charge of the battery, the amp draw and voltage level, the temperature, the time to full charge and the number of charge/discharge cycles. We found this feature to be valuable in monitoring the performance and characteristics of each battery in the battery bank. It was almost equivalent to having a built in battery bank monitoring system like our Link 2000.
Charge/discharge cycles - The LifePo4 batteries have an expected life of 3,000-4,000 charge/discharge cycles at a discharge to 90%. Lead acid batteries have an expected life of 300-400 charge/discharge cycles at a discharge to 50%. During our 6 week cruise we never plugged into shore power and the BMS recorded only 11 cycles. I'm not sure what constitutes a cycle but will research this in the coming weeks. See my earlier blog post for a description of our power usage profile.
Discharge profile - The two battery LiFePo4 house bank discharge profile is significantly different from a lead acid bank. The LiFePo4 bank stayed between 13 and 13.4 volts up to our maximum discharge which was about 75%. We anticipate the bank voltage would have dropped off rapidly at about 90% discharge. A lead acid battery decreases in voltage as more current is drawn. The contrast in voltage drop seemed significant in the performance of our refrigeration (our major appliance). It ran at peak efficiency all the time. While difficult to quantify, it appeared our power consumption in a 24 hour period was less with the LiFePo4 batteries than last year with the lead acid battery bank.
Discharge rate - The BMS built into these batteries has a 150 amp discharge capacity. This means the batteries can sustain a heavy discharge without damage or degradation. Our manufacturer has advised us that the quality of the cells and quality of the BMS is key to the longevity and performance of a LiFePo4 battery. We have seen this firsthand.
Weight - Each 100 Ah battery weighs about 31 pounds. A comparable lead acid battery is about twice that. We replaced a four battery lead acid battery system weighing over 200 pounds with a three battery system weighing 93 pounds.
Safety - Li batteries have a reputation for catching fire. Not so with LiFePo4, a very different technology. The built in Battery Management System monitors the state of charge of each cell group and controls the charge and discharge rates. These batteries have two major components, the LiFePo (Lithium Iron Phosphate) cells and the BMS (computer) the components are housed in a sealed battery case. There are no toxic chemicals or gases as in lead acid batteries. The batteries can be mounted in any direction; bottom or side.
Compatibility - Our key concern in installing LiFePo4 batteries was compatibility with our existing charging systems and appliances. We discussed this at great length with our manufacturer. They reviewed the specs of each of our systems and gave us the thumbs up on compatibility. It appears they were correct as to date we have had no compatibility issues.
Cost - LiFePo4 batteries are 3 to 5 times the cost of lead acid type batteries. Cost justification has to be based on convenience, performance and longevity. It haven't run the numbers yet but based on the number of cycles these batteries can support, there is a break even somewhere around 8 years not taking into consideration all the intangible benefits.
Winter Storage - The LiFePo4 batteries can be stored in temperatures of 20 below zero. It is recommended that the negative terminals be disconnected so there is no chance of draining the batteries while in storage. The good news is that these batteries don't have to be removed from the boat in the winter.
Bottom line - LiFePo4 marine batteries with the configuration we tested are lighter, can be drawn down 90%, hold a steady voltage, are plug compatible, and charge more quickly than lead acid batteries. They are nontoxic and safe. They are more expensive than lead acid.
Contact me anytime to discuss how this technology might be applied to your marine application.
Thomas Trimmer has been cruising with his Ericson 38 sailboat on the Great Lakes for over 20 years. He has pioneered the use of solar energy for wilderness cruising. He is continually designing and building equipment to simplify and enhance the cruising experience.