I’ve also seen similar results when working with long-term outdoor deployments. The low quiescent currents are encouraging, but as you noted, the internal resistance of LiSOCl2 becomes more noticeable as the battery ages, especially under load spikes from sensors or radios. A good-sized supercap buffer really helps smooth that out.
If anyone is considering battery options for these kinds of remote, low-power systems, a 3.6V lithium battery (such as LiSOCl2 cells) is a solid choice due to their long shelf life, wide temperature tolerance, and low self-discharge. They’re not rechargeable, but for field deployments where servicing is difficult, they can easily last several years with the right power management strategy.
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