Lithium battery cycle life

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Lithium battery cycle life

Postby offgridQLD » Thu Oct 20, 2016 9:31 am

Ok so it's not a large stationary storage battery but it is a lithium battery and I think it puts into perspective how incredible lithium battery chemistry is.

My example cell is a 3.7v 5.2whr 1420mah IPhone 4 cell. This cell has been sized to give the phone a full days Average use and charged at the end of each day. How intensive that use is will determine the DOD each night before recharging. I would say personally on average the DOD is around 50% though can be 25 - 90% DOD.
Image
This gives a reasonably high discharge rate when you take the cell size into account. The same can be said for the recharge rate .75A so roughly 0.5C.

I have had this phone from 2010 it's now late 2016. So the battery is now 6 years old. The cell inside has now had 2125 or more cycles on it. I would say the cell is treated harsh in comparison to a stationary large storage cell. The phone is full of hot electronics that are more or less pressing on the cell and the phone is often subject to hot conditions in cars and outside.

So yesterday I did a full DOD cycle test on the cell. The results were 1248mah 12% capacity loss in 6 years and 2125 cycles. :D

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Edit: I had to order a new screen for this phone after my wife almost dropped it over the Hoover dam wall last year (well dropped it on the concrete path at the top of it :lol: ) So when ordering the new screen I also ordered a new OEM battery as well $16. So I plan on installing the new cell in the phone for a day and test it's capacity for comparison and will report back. Though I don't expect it to be more than 1420mah printed on it.



Kurt
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Re: Lithium battery cycle life

Postby Gordon-Loomberah » Fri Oct 21, 2016 3:55 pm

Most are good, but you can get unlucky and have one blow up/burst into flames after a week!

The battery in my wife's Samsung expanded a very disturbing amount after a year or so of use, and we put it in a tin, outside, just in case it went off with a bang.

You appear to have a remarkably good life from that one, Kurt. The average discharge rate isn't very high though- your average 50% DOD over say 15 hours between taking it off the charger in the morning and putting it back on in the evenings is a discharge of (using new specs) 710mAh. Thats a rate of C/30 or 0.033C.
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Re: Lithium battery cycle life

Postby offgridQLD » Fri Oct 21, 2016 4:42 pm

Yes swelling is a good indication things are not good and the cell and it will most likely drain its self flat even when not in use (good move getting it out of the house) I keep all cells not in use in the shed in a box that wouldn't create drama if it went up in flames steel of fiber cement is good. House is free from chemicals and combustibles as much as possible.

Yes that discharge rate sounds correct for a average rate. Though I would say its not a very flat curve over the day. Watching a tube video would be draining the battery at a very high rate (or any intensive application) . Siting in your pocket with the screen blank idle wouldn't be much at all though always have WIFI and Bluetooth, GPS on. I would stll say it would be more intensive than the average offgrid stationary storage overnight. The recharge rate would be to.

I will pop that new battery in tonight when I have access to the special funky screwdriver to get the cover off. keen to see the comparison capacity.

I like using small consumer appliances as some indication as its much easier to clock up lots of cycles and any cycle testing you not dealing with huge numbers.

I have to say the battery's and how the devise manages them has to be improving. I remember laptops from years ago would run so hot and the removable battery's (particularly if they were plugged into wall power 24/7) would be lucky to last a year or two.

I now have a small Asus lightweight laptop (cheap run out I pays $200 for) I got it about 4 years ago and the laptop is on more or less all day. The cell inside isn't removable (though you can replace it if you pull the bottom cover off the laptop) It can still last several hrs on the battery 4 years on. I haven't capacity tested it but I would say it would be lucky to have lost 15% capacity.

That said my wife has a little apple ipod that was purchased about the same time as my iPhone and the battery on that is toast charges in 5 min and lasts about 15min. (very hard to replace as the only way in is to melt the glue off the screen and get at the battery from the front) So I'm not sure why that battery is toast.
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Re: Lithium battery cycle life

Postby offgridQLD » Mon Oct 24, 2016 6:23 pm

I have the capacity results for the brand new cell. I did cycle the cell once before testing. Same method for testing as the old cell. Run the cell down until the phone shuts down on low battery. Then recharge through USB energy meter.

As I kind of expected the phone uses some energy while being recharged at idle. So my the new cell needed more than 1420mah to recharge. 1504mah to achieve 100% SOC.

Old cell 1248mah
New cell 1504mah

17% capacity loss for the old cell over the new one.

I still think the old cell did well and I see no reason why a cell like this it wouldn't come close to say 20% capacity loss after 2500 cycles. Perhaps the results world be even better if I didn't forget and let it bake in the direct sun inside the car in central AU. So hot I almost burn myself picking it up a few times. Jet black phone made of glass and steel.

I don't think I will ever know the extra long term results as I will keep the new cell now in the phone and the old one as a back up.

Kurt
Offgrid 2008, Selectronic PS1 6kw/48v inverter, x 2 Midnite solar classic 150 MPPT, 3960w NE PV 24 x 165w BP panels, 4200w NW PV 21 x 200w DAQO PV, 16x400ah lithium.
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