David, is there a reason why the Tempest is programmed to go into power saving modes below about 2.4 volts? It would seem from the graph you’ve shown that about 80% of the battery power is still remaining.
The Tempest needs a minimum voltage to work. Even though there is a significant amount of energy left, the nature of electronics doesn’t easily lend it self to low voltages. Since LTO cells are so robust, that is why they are used over the former LFP cells used in the first generation SKY Solar Power Assessory. If WF had used two LTO cells in series, there would have been more complexity due to the need for a battery management system to keep the cells balanced. This would undoubtedly increase cost and reduce energy efficiency.