Battery life in wireless applications
People asking us to develop new wireless sensor and wireless networking products but who have very over-optimistic ideas about how small the button cell battery can be regularly contact us. I’m hoping this brief introduction to battery selection will alleviate some of the confusion.
Many electronics engineers use simple calculations to estimate the life-span of a battery based on the average current consumption and the nominal Amp-Hour (Ah) capacity of the battery. For example if they assume an average current consumption budget of 10uA, and they plan to use a 55mAh version of the popular LiMnO2 type of battery, the battery life is approximated by dividing the capacity by the average current consumption. This gives a very respectable, but probably illusory, 5,500 hours and all from a tiny coin cell measuring just 16mm in diameter and 1.6mm in thickness.
Unfortunately, the picture is unlikely to be so rosy. Battery life is heavily dependent on other factors, which include, among others,
Its internal resistance,
The minimum voltage at which the application circuit will work
Discontinuities in the current consumption profile.