@mahonj Actually, they do make cells that size, there are cylindrical hard-shelled lithium-ion batteries of various sizes other than the 18650.* For example, the 26650 is a more popular choice but is only produced by Chinese companies (not large brands like Samsung). *Source: What is an 18650 battery? Yes, the "wasted space" as "cooling channels" seems like a lazy argument but it's quite efficient actually. However there are some more fundamental variables, eg. Economies of scale. The 18650 battery started out inside laptops. It's also in power-tools and so forth. I do believe electric vehicles can drive demand for larger cells but it's very far from being able to do so given the operational set up already exists keeping cost pressure in favour of the cylindrical 18650 design. Modularity is inherently safer, and safety is still the primary concern for shipping and consumer-use going forward.

Very nice energy density but cycle life (200) is low.

Yes! The tugboat, unlikely as it seems uses a lot of energy. All boats do I guess, but especially the work-horses of the sea. Hybrid boats make sense to me.

One year later, and there is no more major publications about the sodium 18650. The thing is, I check Google News every day for articles about these batteries and lithium-ion. You can apply the 80/20 rule here. 80% of the news will be about battery breakthroughs that don't come to fruition and the ones that see production are a decade or more away. I am still optimistic though, there will be something that surpasses lithium-ion. Like lithium air, or these sodium batteries... Right now typical 18650 batteries last about 500 charge cycles. That is, they reach 80% of their original capacity (difference between beginning capacity and current). No where does this article actually define what their cycle life is. The definitions continue to be ambiguous (as other posters mentioned) for just about everything else. So yeah, confirmed fluff. Scientists need PR too! Source(s): Battery Bro - What is an 18650 battery?