This is a rather long-term experiment that started a while ago to try and graph the aging of a power bank’s Lithium Polymer cell. Up to the last part, a total of 100 cycles was run for the experiment, which pushed the power bank to a total of 116 cycles from new.
As it turns out, I couldn’t let the idea rest, so I’ve continually pushed the unit, and added another 50 cycles of data to the set. The power bank has now completed a total of 166 cycles from new, which is about 33-55% of the lifetime of most cells (i.e. 300-500 cycles). This has taken quite a bit of time and effort – so lets see what we’ve discovered.
How did it go?
From the graph, it’s actually done quite well. It seems the capacity decline is slowing ever so slightly, and it’s hovering at about 3725mAh from an initial capacity about 3860mAh. This small level of decrease is actually not that many times bigger than the test to test variations (due to charge termination differences) and isn’t likely to be noticed in everyday use.
It seems that the decline trend is still evident though, so as a result, it seems our test apparatus is able to show the degradation over time, but best as a function of statistical regression of multiple readings. The fit R-squared value is slightly better than before, likely because of more closely spaced readings towards the later readings – this may be due to improved air-conditioning temperature control of the test room.
The approximate decline in capacity is 0.6857mAh per cycle … and thus the 80% cycle life estimation based on the linear regression is now up to 1120 cycles! In reality, it’s not that likely it will reach such a high value, but it’s another indicator that the rate of capacity decline is falling.
Represented on a scale starting from zero, it’s evident how little capacity has been lost so far.
While it’s a rather interesting and tedious experiment that I intend to continue into the future, unfortunately the runs will be done less frequently than before due to lots of research commitments during the December-January period. I will probably still run the experiment after those commitments, but at a reduced rate of about one cycle a day, as I won’t have the time to tend to the experiment. The next update will come when we’ve reached 200 cycles in the experiment (for 216 cycles total).