Why we don’t have Lithium Batteries
I am often asked if we have changed to Lithium batteries, and those who know us are frequently surprised when I say, “No.” We certainly have a technology heavy boat, and are not put off by the new approaches to systems that work for us. We posted a long form description of changes we made to our electrical systems on board Harmonie a few years ago in this blog post:
There are several reasons why we have not jumped on the Lithium bandwagon that I would break down into four categories:
- Administrative
- Technical
- Economic
- Performance
Let’s dive into these and explore them a bit.
Administrative
We just completed a long and painful round of shopping for insurance. (That’s a WHOLE other blog entry for that!) After much back and forth, we found ONE company that was willing to write us a policy that we were happy with, the same one we have been with for the last 6 years. They have some rules about Lithium battery installations. The batteries must be supplied by a US based company, and they must be installed by a certified, professional, installer. These rules make sense from the underwriter’s perspective.
The rule about US only suppliers has two reasons. First, many people are sourcing raw battery packs from unknown, unvetted suppliers in China for DIY batteries. The quality might be great, and might be terrible, there is simply no way to know. In addition, if something goes wrong in a way that results in a claim, there is zero likelihood that the insurer could ever recover any money from a Chinese supplier.
I have seen many postings on the web from people who are doing their own installations of Li batteries. The level of ignorance is profound. Some of these people do not know an Ohm from a Watt. They have no idea the risks they are taking or how to mitigate the risk. Many of these installations are being done by people who are adding things like electric cooking which are high amperage consumers of DC power. A quick look at insurance claims data show that high amperage DC power circuits are one of the most common causes of boat fires. The requirement that a knowledgeable installer be used for major modifications to an electrical system seems to make perfect sense to me. In the event of an installation error causing a claim, they again have a third party to try to recover some costs from.
Oh, did I mention that the underwriter of our policy bumps the premium up 20% for all boats with Lithium battery systems?
So, our insurance situation pretty much keeps us out of the Lithium market for the foreseeable future. This might not, apply to you. Before you commit to a battery change, be sure you know.
Technical
Really, there is just one big one here. We have a battery box that holds eight G31 batteries, for a total energy storage of about 425 Amp-hrs at 24 Volt (10.2 kW-hours). We could simply drop in eight G31 sized Lithium batteries, and be in the same ballpark. But… a bank of “drop-in” batteries of this combined capacity are typically limited to a total current draw of no more than 400 Amps. This is a problem for us, since our bow thruster is powered from this battery bank, and it draws 485 Amps. Realistically, we would need a system that could supply at least 500 Amps at a 50% duty cycle for at least 5 or 10 minutes.
This power limitation is not from the Lithium battery packs themselves, but rather on the internal Battery Management system used in these “drop-in” batteries. A way around this is to use plain Lithium batteries and an external Battery Management system, but now there is a more complex issue around the shape of the batteries and the geometry of the available box. It is not insurmountable, but it is a complication that limits the available options. It gives a more sophisticated and reliable system, but also significantly increases costs.
Economic.
One of the things that remains always true: Batteries are energy storage systems ONLY. If you use 12 kW-hrs of energy per day, you somehow need to generate 12 kW-hrs. That doesn’t change no matter what kind of batteries you use. Now Lithium batteries do have a significant advantage here, they can accept high charging rates, right up until they are almost full.
When our gel batteries are as deeply discharged as we allow them to go, our generator takes 2 hours to bring them up to 95% full. Most days the generator does not run this long, but let’s say it does. The first half of that charging time is spent at full output, and during the remainder of the time the output is tapering off. If we had Lithium batteries, that 2 hours would be reduced to about 1.5 hours. Our generator uses about 2 liters of fuel an hour. So we’d save about 1 liter of fuel a day. Current price for diesel fuel in the Bahamas is about US$6/ gallon, or about US$1.56 per liter. Given the full-on capital cost for an upgrade to a Lithium battery system for our boat would be on the order of $5,000, the payback period of over nine years, doesn’t really seem a good investment.
The economics of a Lithium change have gotten more attractive, and continue to do so, as the costs of the batteries come down. However, much of the cost a a good lithium upgrade are in ancillary systems, and those prices do not show the same downward trend.
Performance
In almost all ways, Lithium battery performance specifications are, at least on paper, WAY better than any flavor of lead acid batteries. But you always have to ask, are they changes that matter in the real world, and for the way I use MY boat? Let’s look at some of these.
Weight. Hands down, Lithium batteries are way lighter than lead. It is not even close. For many cases, this is an important consideration. But for our boat, it is actually a negative. The weight of the lead batteries on the starboard side balance the weight of the generator on the port side. This is not a make or break issue, but it is enough to say that for us, the better power to weight ratio of the Li system is not a benefit.
Voltage Sag. Again, no question, Li batteries are better at supplying high currents without the voltage dropping. But this has always had me scratching my head about why I should care? All our systems work fine with the lead batteries. So what, exactly, would the performance improvement be that I would actually see and measure in retrofitting a functional system?
Higher Usable Capacity. Li batteries are certainly more robust in this regard. Lead batteries suffer if discharged below about 50% of their rated capacity. So the “usable capacity” is a bit less than half of the name plate. With Li batteries the “usable capacity” is probably closer to 70% of name plate. Is this important to you? It depends. Our generator is tied to our battery monitoring equipment. When our battery bank drops to the minimum state of charge we set, the generator starts automatically, runs until they are about 95% full, and then stops, automatically. We frequently don’t even notice it has happened. I realize that boats that do not have this feature struggle with manually initiating charge in a timely manner if the battery back is on the small side.
Our existing system easily runs a two burner induction plate AND a small electric oven to fix dinner. It can power an air conditioner to cool our sleeping cabin. So what capability–exactly–would we gain with a Lithium system? The generator would run less often, that’s true, but it would run for basically the same total time, since the amount of energy needed would be the same. For day to day operation, we’d see almost no change in the way we use our energy on board.
Conclusions
For the way we use our boat, the benefits of changing to a Lithium system do not outweigh the costs. These conclusions are ONLY valid for our boat. For other boats, a Lithium system makes perfect sense and a lead battery would be a poor choice.
Certainly we have no motivation to rip out a gel battery bank with a long life ahead of it to install a lithium system. If we need to replace the gel batteries in the time we own this boat, it might be true then that a Lithium system makes sense, or maybe something else completely different will be available.
For some people, who are reaching far beyond what their original electrical system was designed for (if it was actually designed at all!) a lithium battery bank can make life a lot easier on the hook.
Many people are switching to lithium batteries for whom the advantages are small, or even nonexistent. They are told they “need” a lithium system to cook with electricity. Not true. Or their expectation is that a lithium system will somehow greatly reduce generator run time. Or maybe they just need the latest cool toys.
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