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I'm currently integrating a coin cell power design into an electronics project. I am trying to verify my understanding of the 'continuous standard load' rating given for a battery (datasheet)

When looking through coin cell data sheets, I am typically looking at the mAh rating. This is a a measure of how much current can be supplied for a given time period (sort of). Now, I also understand that this number is typically provided given that you operate at some spec'd current. That is, if you decide to draw more current than the spec'd current, the battery will not be able to last as long as the mAh rating suggests.

So my question: Is the 'continuous standard load' the coin cell current that will provide the spec'd mAh rating? Furthermore, if I run above this current, will that translate to a much lower mAh rating?

The reason I'm confused is due to the fact that the 'continuous standard load' is such a small number in the datasheet I'm referencing. When looking at the CR2032 coin cell in the datasheet, it has a mAh of 225, but it only has a continuous standard load of 0.2mA. If I operate at say 10mA, will that translate to something much lower than 225mAh?

Thanks!

Izzo
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2 Answers2

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If I operate at say 10mA, will that translate to something much lower than 225mAh?

Certainly, yes. I'd even say you should find a different battery for your application, as CR2032 is not suitable for such high currents.

Take a look at the following graph from your datasheet:

enter image description here

Even at 1.5mA, you're going to lose between 12 and 33% of nominal capacity. The cell wasn't characterized at 10mA, but extrapolating the graph I'd say you'd be lucky to get 30-50% of usable capacity in the optimistic case. Realistically, the cell may simply fail from overcurrent after a few hours of continuous 10mA load.

Dmitry Grigoryev
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  • Great information. So my biggest design constraint is form factor - the smaller the better. And because this is a personal device in which I can swap out batteries, the small size trumps the costs of having to replace batteries. So my question, is there an easy way to search for high current rated coin cells? There doesn't appear to be any kind of sorting options on Digikey, Mouser, etc. Why is this rating not typically listed? Surely it appears to be very important. – Izzo Oct 07 '16 at 13:48
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    Actually, my extrapolation might be a bit off (it's an extrapolation after all). You may want to read [this paper](http://www.ti.com/lit/wp/swra349/swra349.pdf) from TI on coin cells. – Dmitry Grigoryev Oct 07 '16 at 13:55
  • Also, not all CR2032 cells are the same. [Here](http://data.energizer.com/PDFs/cr2032.pdf)'s one form Energizer, rated at 400 Ohm (almost 10 mA) discharge pulses of 2 seconds. – Dmitry Grigoryev Oct 07 '16 at 14:00
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The continuous standard load is the amount of current output that the battery can sustain for more-than-brief periods of time. The mAh rating is actually a unit of charge, and that tells you how long a battery can provide a given current.

For the first battery on that linked data sheet, the continuous standard load is 0.1mA and the capacity is about 30 mAh. Thus if you're drawing .05mA continuously, you can expect the battery, if it started fresh and hasn't been abused in storage, to last for 30/0.05, or about 600 hours of total use.

Depending on how critical your specs are, you might consider derating the capacity to about 80%. Rounding to the nearest hundred hours, that would give you about 500 hours of use at half the recommended sustained load.

Scott Seidman
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