Zippy Battery Capacity Test After Eighteen Months of Storage

I had an opportunity to let my 4.2 AH Zippy battery sit unused after I last charged it on February 26 of 2013 — that was eighteen months ago.

I had noted in earlier testing that the Zippy self-discharge seemed to be about 2X higher than other LiFePO4 batteries I’ve tested in the past, but speculated that the self-discharge rate might calm down after time.  But as my most recent test illustrates, the self-discharge stayed about the same — 3.8% per month.  At the end of eighteen months, the Zippy battery still had 1.3 AH remaining.  That’s 32.5% of its original capacity, or a loss of 67.5% (3.8% per month).

Battery test @ 2.1 Amp Discharge (C/2) following six months of storage.

Battery test @ 2.1 Amp Discharge (C/2) following eighteen months of storage (graph incorrectly labeled “Six” months).

NOTE:  The graph above is incorrectly labeled.  While it says “Six Months” in reality it was 18 months of storage (since Feb 2013).  And even though the battery is marked as “Failed”, note that it was still above 13 Volts after 18 months of storage, and still had 33% of its original capacity.  While not as good as a primary Lithium battery (15-20 years of storage life), being able to set a battery aside and ignore it for 18 months is still pretty impressive.  Do that with a SLA battery and it will be totally dead and won’t recover.

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