When designing an ultra-low-power device that is powered by a primary lithium battery, is it necessary to include over-voltage protection?
Specifically, I am using a Microchip (Atmel) SAML21J which specifies a supply voltage of 1.62-3.63V.
I am using Lithium-Thionyl Chloride (Li-SOCl2) batteries with an open circuit voltage of 3.65V.
In practice, I've never worried about the small potential over-voltage in testing on the bench, both because the voltage immediately drops slightly with load, and presumably the microcontroller can tolerate short-duration small over-voltage. However, as I look at other components with a max voltage rating of 3.6, I wonder if there is value in adding, say, a Zener diode to clamp the voltage.
The factors against adding protection in this case are 1) cost, and 2) potential battery life decrease.
I'm mainly concerned that brand-new batteries installed during production could cause damage to some percentage of finished units.