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Tech Talk with SeaBits
THE NUTS & BOLTS OF LITHIUM by Steve Mitchell POWER SYSTEMS Lithium battery systems have become increasingly popular in the last few years, and offer a wealth of benefits for boats. However, there are some considerations that extend beyond the batteries themselves that you should know about for a safe and performant system. The most common type of lithium battery is LiFePO4, or Lithium Iron Phosphate. They’ve been around for a number of years in the marine world, but where you’re probably more used to seeing them is in consumer electronics. Smartphones, tablets, and laptop computers have used this technology for many years. They are considered very safe if used appropriately, and good marine systems include additional steps to enhance this safety. One common theme I hear from potential customers is that lithium batteries are unsafe, and that they could melt a hole through your hull or burn your boat down. While there have been examples of this, you can probably find more fires and sinkings of boats from poorly wired electrical systems and other more common problems. There are many systems that could cause a catastrophic issue on a boat, and if installed properly, a LiFePO4 battery has little risk of being one of those systems. Here’s a rundown on types of lithium batteries and some things to keep in mind if you’re considering making the switch. LIFEPO4 ADVANTAGES LiFePO4 battery banks have a few major advantages that are applicable for boating: weight, charging capability, and overall life. A typical GC2-type flooded battery weighs in at around 60 pounds, and an identical LiFePO4 version is about 30 pounds. The weight savings will equate to lower fuel consumption, and in the case of distributed banks, opportunities for better trim and handling. They’re also a heck of a lot easier to move around! Using the same GC2 battery, in a flooded cell you’d have somewhere between 200 to 220 amp hours, but only 50-percent of those are usable, resulting in 100-110 total. The same LiFePO4 battery would have about 100 amp hours, the vast majority of which would be usable. So, while you’re not getting more amp hours with lithium, you are getting the same amount in a lighter package. Charging is where LiFePO4 gets interesting, particularly the higher rates that they are able to accept in general. For flooded batteries, a good estimate is that your maximum charge rate is 20-percent of the overall amp hours. Continuing to use our GC2 battery example at 200 amp hours, and we would 48º NORTH
be able to charge it at 40 amps safely. The same GC2 LiFePO4 battery could be charged at 100 or even 200 amps (depending on manufacturer and type), which would greatly reduce generator and charging time. Charging LiFePO4 is A standard Victron 300 amp hour also more efficient than lithium battery. a flooded or AGM battery in that there is really no float stage, and the battery can be charged at the maximum amount right up to the final amp hour. If you’ve ever watched your battery charger progress on a flooded or AGM bank, you’re very familiar with the last 10 to 20 percent of capacity taking forever to finish. LiFePO4 doesn’t have this disadvantage and that results in far more efficient and faster charging for that last 20 percent. The final major reason folks gravitate towards LiFePO4 technology is the overall life, which is a somewhat controversial topic. These batteries are designed to last anywhere from 1,000 to 3,000 cycles depending on the manufacturer, or an estimated lifespan of 10 years based on some calculations. That assumes pristine conditions, good charging amounts, etc. — and doesn’t account for some of the extremes in the boating world. Comparatively, AGM batteries average about 500 cycles and last an average of six years. CHALLENGES The biggest challenges in choosing LiFePO4 include price, temperature, charging, and complexity. Price is likely to be the first hurdle for most boaters when considering LiFePO4. A standard flooded GC2 battery will run you about $175 to $200. A similar GC2 LiFePO4 battery will cost $900 to $950, which is a significant premium. You have to weigh that against the pros above, specifically that of the longer life and higher charging cycles. Many LiFePO4 batteries are also more temperature sensitive than their flooded and AGM counterparts. That’s not to say that temperature extremes don’t affect those types of batteries — any extremes will dramatically reduce the life of any battery technology. But LiFePO4 in particular do not like super cold or
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FEBRUARY 2021
