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  • Author Author: mlease
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The 10 year battery life – myth or reality?

mlease

Myths and legends are usually the subject of incredible beauty, unsurpassed strength or attempting what mere mortals assume is an unobtainable goal. It is often difficult to separate myth from reality or even know where one ends and the other begins. The same can be said for much of what you read these days about products with a 10 year battery life. When you see advertisements for wireless devices claiming 10 year battery life from a coin-cell battery it is easy to think that is the stuff of myths and legends. Yet, given the right hardware/firmware design and the appropriate battery technology and capacity for a certain application, 10 year battery life is certainly a doable thing.

 

Read the complete post at http://cmicrotek.com/wordpress_159256135/?p=239

  • 10 year battery life is achievable, given the right battery type.  With some batteries, the self discharge alone will fully discharge them in less than 10 years.  And yes, you need to be careful of the meter used to measure the current. 

  • in reply to mlease

    Agreed.

     

    Personally I find nearly all claims to long battery life with speculation until I have fully read the reasons why and care and feeding of the device to achieve that marketing number.

     

    If I design a product and the average use can run ten years, I would still request my users to replace the battery every five years just to compensate for unusual use and the possibility that not all batteries are the same.

     

    DAB

  • in reply to crjeder

    I've seen CR type coin cell battery data sheets that call out a self discharge rate of 1% per year. Looking at it another way, "shelf life" for a CR coin cell battery is usually spec'd as 80% of capacity after 10 years so the self discharge could be calculated from that for a given capacity. Of course, it isn't really as simple as that and temperature in particular can significantly reduce the useful life of the battery.

     

    Jack Ganssle has done a lot of experimentation with coin cell batteries. If anyone is serious about getting long battery life from a coin cell check out the link below (and other articles on his website) and his articles on www.embedded.com.

    Hardware and Firmware Issues in Using Ultra-Low Power MCUs

  • in reply to DAB

    My first digit wrist watches battery lived longer than it's case. It broke in two pieces and I kept the watch in pencil case for years until Ilost it.

    BTW: How much is the self-discharge of a coin cell?

  • in reply to DAB

    I expect that radio was from the good old days when mechanical on/off switches were the norm. Many, if not most, of our electronics gizmos today are never really turned completely off.

     

    The main point I was going for is long battery life, even 10+ years can be achievable but someone trying to do that should not go into it thinking it will be easy. Some of the advertisements and app notes (particularly on low-power wireless MCUs) give the reader the impression you can just hook up their device with a coin cell battery and get 10 years of battery life. In some cases performance specs like active/sleep duty cycles may have to change or a different battery type selected in order to meet a battery life target. It is probably fair to say as the complexity of a product increases or the more variable the operating conditions are, the engineering effort required to achieve ultra-long battery life increases exponentially.

    A second point is that many engineers aren't equipped to accurately measure the ultra-low sleep mode currents required to achieve ultra-long battery life. I would encourage any engineer attempting this to work through the voltage measurement accuracy calculations in their scope manual before placing much trust in their current measurements. If you are trying to measure several millivolts across a sense resistor with even a 10 or 12 bit digital scope the measurements could be wrong by several millivolts.