We have been using a 735 amp hours (12V) battery bank which lets us operate most of our electric needs without requiring the use of our diesel generator for a couple of days at a time. We have solar panels which help add a few amps back into the system every day. When we need to use the more power hungry items (like the microwave, air conditioners) we have to use the generator.
Our current main battery bank (shown above) is showing signs they need to be replaced. When we first went to buy our boat in 2008, I was interested whether new Lithium Ion batteries used for electric cars were available yet for boats. [UPDATE 6PM] The particular version we are looking at are Lithium Yttrium Iron Phosphate which are particularly safe – with almost no risk from fire, or exploding like earlier Lithium-based batteries. These batteries (like the ones in your laptop) have fantastic qualities for our needs. They can be charged much faster, they can be deep cycled (used) to more than twice the amount of typical marine batteries, and they can be cycled many more times than standard batteries (so they will last longer). Not only that, but the batteries take up far less space, and weigh much less than traditional batteries. Weight is a big factor for sailing catamarans. In 2008, the only Lithium Ion batteries on the market were prohibitively expensive for marine applications. At that time, I got quotes for more than 300% the going rate for high-end traditional batteries (AGM).When we heard about Tahina’s sister boat s/v Sirius in New Zealand, I was excited to learn that her new owner Mike had recently purchased Lithium Ion batteries. He told me that the price of the batteries are much more reasonable now. When we were in Fiji, I actually had a chance to see his installation as shown in this photo. Notice how much less space they take in the same location under our salon couch seats. Now that our current batteries are going bad, I’m in the process of getting a quote from the same New Zealand outfit that delivered the batteries for Sirius.
Here’s a summary of the benefits to the Lithium Ion battery bank of 600 amp hours we are looking to purchase:
- The new batteries will take up about 1/4th the space of the originals
- They weigh over 200 pounds less than our current batteries. This benefit is especially beneficial to catamarans which are weight sensitive (effects sailing performance).
- Although fewer total amp hours than our current bank we will get more useful amp hours. We will get over 400 amp hours of usable power for each cycle (since we can use them down to 30% of remaining charge). With our current battery bank we would only use about 300 amp hours, because those batteries could only go down to about 65-70% of their rated amount (without damaging life cycles and our voltage would go down too far – below 12 volts).
- The lithium batteries hold a higher voltage under load than the regular batteries. They maintain that voltage even as they are discharged. Sirius now sees 13+ volts all the way until it is time to recharge the system.
- By using “only” 70% of the power, the new batteries are rated to 7000 cycles. This is more than twice our current batteries. If the batteries actually last that long, we recover far more than our investment.
- The new batteries can be charged a much higher rate. They can handle up to 300 amp hours of charging. And, the absorption period for topping off the batteries is correspondingly higher as well. This means the total time for us to re-charge the system is much less resulting in less diesel fuel being used to charge.
The new batteries will be more expensive than our last set. However, only about 25% more expensive. And, the prices are still coming down for the Lithium batteries. In my estimation, we will easily recover the extra expense. First, by saving diesel fuel since the system will recharge faster, and we will have to charge less often (we’ll probably recover the extra cost in the first year alone from that factor). Second, because they are rated to last more than twice as long as our existing bank.
The new bank can operate with our existing charger and charge controllers. However, we will need to buy a new monitoring system since you can’t tell as easily how deep they are discharged based on the voltage. This adds another few hundred dollars to the purchase, but is worth it to help protect the investment.
As with any decision, there are some risks involved. The biggest risk is that this technology hasn’t been used much in boating applications. However, the fact that it has been used for millions of cars and other electronic devices reduces that risk. We won’t know whether the batteries will reach their life cycle estimate because no one has had these new models long enough. We similarly won’t know whether the company the batteries are coming from will honor warranty issues. Hopefully that risk won’t be a factor, but if it is, the fact I am a widely read technology writer might help. And, finally of course, we are spending more than traditional batteries would cost. However, as a technologist, I’m willing to take that risk for what I feel is a superior technology.
This is the next major advancement in battery power for boating. I think it will improve the quality of our life on board, and provide us with a reliable and improved power system. If not, we’ll have something else to write about on the blog.