Electronic – Panasonic Eneloop BK-3MCC (4th gen) – where I can find maximum discharge current

Quick Rules of Thumb

1. 10mA is your maximum current draw.
2. Buy fresh batteries. Always verify this by running lifetime tests on your batteries when you buy from a new supplier, or a new batch.

Our General Conclusions

When testing with coin cell batteries at my last job we found a number of things:

1. Surpassing 10mA per cell greatly reduced battery life.
2. 20-30mA was normally around your "maximum" current you could draw, but this is not dependable, the 10mA line being the highest current we could pull for deterministic function.
3. 1mA was as high as you could go without significantly degrading rated capacity(get nearly the published capacity).
4. Staying below the .1 mA suggested line would normally meet the rating of the capacity.
5. Someone selling you old batteries can do more to harm your tests than almost anything else. The batteries purchased directly from china gave the best results, the nice company in new york had battery cells that performed worse that batteries we had on site in storage for 4 years.

Capacity Rating

These results all seemed relatively consistent across different rated capacities, giving the same results with 50mAh batteries and 400mAh batteries. We chose to use 200mAh batteries on devices that needed to pull 20mA, they would significantly outperform 800mAh coin cells(the big ones you can buy) as passing 10mA hurt the battery life significantly.

When we passed the 10mA line the lifetime of the battery had a very large variance, we attributed this to manufacturing differences, but the same batch could have vastly large differences.

How I know this.

We did testing on batches of 20-50 coin cells to choose our rating and package. After this point we ran tests on more than 500 batteries under different conditions to verify results and predict lifetime. We ran tests where the current was pulsed, tests in different temperatures, and tests were we let devices run for months to try to test what our expectation would be. I am sorry I do not have references, as this testing was done at a company and was not published in any form, I have nothing I can reference for this.

The calculation is straightforward. The capacitor size is simply a question of how much voltage drop you can tolerate over the duration of the pulse. The average current from the battery is a function of the duty cycle.

ΔV = I × Δt / C

Solving for C gives:

C = I × Δt / ΔV

Let's assume you can allow ΔV = 0.1V. For your first example, this works out to:

C = 25 mA × 25 ms / 0.1 V = 6.25 mF

The average current draw is 25 mA * 25 ms / 2.5 s = 0.25 mA.

For the second example, the numbers work out to:

C = 50 mA × 100 ms / 0.1 V = 50 mF

Average current = 50 mA * 100 ms / 1.0 s = 5 mA.