This year, we upgraded our boat's battery system from lead-acid to LiFePo4 (Lithium Iron Phosphate) batteries to explore their performance in a marine cruising environment, especially in relation to our solar power system.
Battery Configuration
After thorough research, we selected custom 100 Amp Hour (Ah) LiFePo4 batteries, each equipped with a 150-amp draw Battery Management System (BMS) and Bluetooth monitoring. Working with our manufacturer, we designed these batteries to withstand marine conditions. Our previous house bank of three 110 Ah lead-acid batteries was replaced with two 100 Ah LiFePo4 batteries, and our 110 Ah lead-acid starter battery was replaced by a single 100 Ah LiFePo4 battery. Our charging setup includes:
- A 75-amp Balmar alternator with a smart regulator
- A Xantrex 55-amp inverter/charger for shore power
- A 175-watt solar system with an EP Xtra-N Li-compatible solar controller
Thanks to the 90% safe discharge capability of LiFePo4 batteries (versus 50% for lead-acid), our two 100 Ah batteries provide nearly the same usable capacity as our previous three-battery bank.
Summary of Findings
Our new batteries exceeded expectations. They handled heavy charging and discharging loads smoothly, integrated well with our existing charging systems, and performed reliably with all our onboard equipment. While the initial cost is higher than lead-acid batteries, this is offset by their longer lifespan. Here are some specifics:
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Bluetooth Monitoring: Each battery’s Bluetooth feature provides real-time monitoring via a smartphone app, showing charge status, amp draw, voltage, temperature, time to full charge, and cycle count. This feature proved invaluable for tracking each battery’s performance, much like having a built-in monitoring system similar to our Link 2000.
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Charge/Discharge Cycles: LiFePo4 batteries offer an expected lifespan of 3,000–4,000 cycles at a 90% discharge, compared to lead-acid’s 300–400 cycles at a 50% discharge. Over our six-week cruise, we recorded only 11 cycles without ever needing shore power. (We’ll be looking into what constitutes a full cycle in the coming weeks.)
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Discharge Profile: The LiFePo4 bank maintains a steady voltage (13–13.4 volts) even up to about 75% discharge, unlike lead-acid, which gradually drops voltage with usage. This steadier voltage made our refrigerator—our largest appliance—run at peak efficiency, potentially reducing overall daily power consumption compared to our previous lead-acid setup.
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Discharge Rate: The batteries' 150-amp discharge capacity, managed by the BMS, supports high-demand loads without degradation. Our manufacturer emphasized that both cell and BMS quality are critical to LiFePo4 longevity, a claim we’ve seen supported firsthand.
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Weight: Each 100 Ah LiFePo4 battery weighs only 31 pounds, roughly half the weight of a comparable lead-acid battery. By switching from four lead-acid batteries to three LiFePo4, we reduced our system weight from over 200 pounds to 93 pounds.
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Safety: Unlike other lithium technologies, LiFePo4 batteries are stable and have a low risk of combustion. The BMS monitors each cell group’s charge and discharge rates, ensuring safety. The sealed, non-toxic battery case also allows flexible mounting positions, and there are no hazardous chemicals or gases involved.
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Compatibility: Before installation, we worked closely with our manufacturer to verify compatibility with our existing charging systems. So far, we have encountered no compatibility issues, confirming their assessment.
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Cost: Although LiFePo4 batteries are 3–5 times the cost of lead-acid, their longevity and performance offer a strong case for long-term value. A rough calculation suggests a break-even point at around eight years, not accounting for other benefits.
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Winter Storage: LiFePo4 batteries can be stored at temperatures as low as -20°F (-29°C). We simply disconnect the negative terminal during storage to prevent any discharge, eliminating the need to remove the batteries from the boat for winter.
Bottom Line
LiFePo4 batteries bring substantial benefits: they’re lighter, offer 90% usable discharge, hold steady voltage, integrate easily with existing systems, and charge faster than lead-acid batteries. They are also safe and nontoxic, though more costly upfront.
If you're considering a similar upgrade, feel free to reach out—I’d be happy to discuss how this technology could benefit your marine setup.
— Tom