Very pleasant surprise regarding my old Molicell 26700's

[Bimmerboy]

It's gotta' be roughly 15 years, or getting close since I bought 7 of them used, weld marks and all, from a fellow CPF'er. They all arived charged at about 4.1V. At first, there were plans to use them in some high power builds, then life got in the way, and I've been meaning to take them out for years just to see if they have any voltage left at all. Well, I finally did.

Got out the multimeter, and my heart sank as the first one tested at 1.9V. Started thinking they might all be ruined by now. However, my spirits were lifted when the next six all tested between 3.7 to 3.9V! Now get this... they've never been charged since I got 'em! Didn't fit my charger.

I'm kinda' psyched about this, and am feeling inspired to finally use some magnet wires I bought, also years ago, and make some adapters to fit the same old chargers I still use... a couple old Pila IBC's (I have two). If the Moli's can still deliver high current, perhaps I'll use them in a crazy mod one day. Wish me luck!

 

[jtr1962]

Interesting. I think the fact you never charged them is the reason they appear to be still viable.

I'm concerned more with calendar life than cycle life as in most of my use cases it might take decades to reach cycle life. Most of my reading on the subject has been calendar life of LiFePO4 cells, not the more usual nickel-manganese-cobalt variety. Here's a good read on the subject, and a lot of the general information applies to other lithium cell chemistries:

The Degradation Behavior of LiFePO4/C Batteries during Long-Term Calendar Aging

With widespread applications for lithium-ion batteries in energy storage systems, the performance degradation of the battery attracts more and more attention. Understanding the battery’s long-term aging characteristics is essential for the extension of the service lifetime of the battery and the...

www.mdpi.com

Of interest is Figure 12 in Calendar Aging Modeling section. High temperatures rapidly accelerate aging. At a 50% SOC and 55°C the calendar life until degradation to 80% capacity is only 1.056 years. At the same 50% SOC and 25°C calendar life increases to 23.8 years. If we store the cells at 10% SOC instead at 25°C calendar life is an astounding 45+ years! At temps under 20°C, which would occur in basements in most of the country, calendar life would be increased even further.

Short version-if you store unused cells in a low SOC at cool temperatures they should be viable decades later. I had some A123 cells I bought c. 2006 which made the mistake of storing fully charged. About 2 years ago they tested at less than 80% capacity. I managed to revive them almost back to where they were by holding the cells at 0% SOC for a few days, as described here:

Capacity Recovery Effect in Commercial LiFePO4 / Graphite Cells

 

[Bimmerboy]

Excellent info, J. Though the Mollies are IMR, I'd say they've been stored at a constant average of 21 - 22°C throughout the years. Hopefully they've had similar benefit from an easy life... thus far. 😜

Still want to build a portable monster quad LED (in series) on a computer heatsink using an old buck driver from TaskLED (I forget the name offhand), and five of these Mollies. I'm guessing they should be able to supply enough juice for the application.

 

[vicv]

Would definitely be a good idea to do a capacity, and possibly impedance test though. Voltage is only one small indication