# LiFePO4 Cycle Life



## kublikhan (Nov 12, 2008)

Hello. I recently heard about LiFePO4 battery technology and am interested in the cycle life and current draw of these batteries.

I found a spec sheet for a ThunderSky LFP260AHA that lists the batteries as lasting greater than 4,000 cycles @ 70% dod, max discharge current of 2C, standard discharge current of .5C, Impulse current of 10C. As I understand it, I would have to limit my discharge current to .5C to reach 4,000 cycles? Is that accurate? What kind of cycle life would I expect to get out of the batteries if I instead drew 2C current from them? Or 1C? Any data on the shelf life? How long could I draw the impulse current of 10C without degrading the battery's cycle life? Would it be enough to accelerate an EV to highway speeds, or to climb a modest hill?

I am curious if ThunderSky batteries would work in a vehicle like the GM Volt. GM is offering a 10 year, 150,000 mile warranty on the battery pack. But most places I find are only offering 1 a year warranty on the battery, if that. Can a ThunderSky realistically be expected to last as long as 10 years, 150,000 miles(going from 80% to 30% dod)?


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## favguy (May 2, 2008)

Some very good questions! If you only draw .5C most of the time and only discharge down to 70%dod, they could feasibly last 4,000 cycles. The thing is no one has been running any for long enough to find out yet, and it seems we can't believe what the manufacturers tell us! As for a 10 year life, again, could well be possible, but we'll have to wait a few more years to know for sure. I'm personally going to risk a pack of 40 or so 160Ah's once I've saved up enough next year. There have been a few, particularly in Australia who have been using the Thundersky Lifepo4's for a year or so now, with a locally built BMS and charger, results so far are very good, I'm watching them like a hawk!

Regards

Paul


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## HDS (Aug 11, 2008)

I found a spec sheet for a ThunderSky LFP260AHA that lists the batteries as lasting greater than 4,000 cycles @ 70% dod, max discharge current of 2C, standard discharge current of .5C, Impulse current of 10C. 


I hate to have my newbie showing, but what is 2C, .5C, & 10C? Is C 100 (in this case amps)? 

I feel like I have to buy a vowel.


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## ClintK (Apr 27, 2008)

HDS said:


> I found a spec sheet for a ThunderSky LFP260AHA that lists the batteries as lasting greater than 4,000 cycles @ 70% dod, max discharge current of 2C, standard discharge current of .5C, Impulse current of 10C.
> 
> 
> I hate to have my newbie showing, but what is 2C, .5C, & 10C? Is C 100 (in this case amps)?
> ...


Common question around here actually . C is the capacitance of the battery. So if the battery is rated .5C standard, 2C max, and 10C impulse, and the battery's capacity is 200Ahr, then you'd get:
Standard = .5*200 = 100 Amps
Maximum = 2*200 = 400 Amps
Impulse = 10*200 = 2000 Amps

Or if the battery's capacity is 40Ahr...
Standard = .5*40 = 20 Amps
etc... etc...


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## HDS (Aug 11, 2008)

Thank you, ClintK, that one was bugging me.

HDS


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## david85 (Nov 12, 2007)

Hmm, thundersky has updated their specs. Before they claimed only 3000 cycles @ 70% DOD.


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## ClintK (Apr 27, 2008)

david85 said:


> Hmm, thundersky has updated their specs. Before they claimed only 3000 cycles @ 70% DOD.


The change is in a good direction.


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## david85 (Nov 12, 2007)

Agreed....

I just got an Email reply from a guy that converted his motor bike to run on TS batteries and he says he's around 300 cycles now and in his words, they have the same power as day one. I dropped him a few months ago and he had less than 100 cycles on them back then. He's very happy with them. His bike is freeway capable and its his current daily driver/commuter whenever weather permits.

I've been trying to contact other back yard (other than dealers) EV'ers that are using thundersky batteries or similar LiFePO4 chinese products and so far, no one has said anything bad about them. Makes me feel a little better about my project.


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## bblocher (Jul 30, 2008)

david85 said:


> Hmm, thundersky has updated their specs. Before they claimed only 3000 cycles @ 70% DOD.


It appears this is only on the 200+ Ah batteries. The 160s I'm considering still say 3000. Also all the batteries smaller than the 200s are still showing 3C constant vs the 2C constant, however, the 200s and over are saying .5C for the 4000 cycles at 70% DOD vs the only .3C for 3000 cycles at 70% DOD.

My question is did they change the 200+ cells or are they going to rerate all of the cells this way? I'd much rather see the .5C rating for extending the life on the smaller batteries too


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