Calendar Life & LFP

[zamboni]

I really hope this is a straightforward question. I've read repeatedly that with Pb batteries there is cycle life and calendar life. "The weight and the warranty", as it's been said. That whole explanation makes solid sense to me. The spiel about how cycle life is measured in a lab and doesn't reflect real-world usage has similarly been well-explained already.

So, what about LFP. Does warranty = calendar life there too?

Given that the tech is young and the warranties are known for being largely unenforceable, I thought it made sense to ask. Is there a kind of all-purpose assumed calendar lifespan for LFP prismatics that experts on this forum use? Like the way 3.65VPC is used regardless of what the published discharge curves say?


- Jerud
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1220W array / 1000Ah LFP house bank
MidniteSolar Classic, Magnum MS2812
ME-RC, Trimetric, and JLD404
2001 Fleetwood Prowler 5th wheel 25 foot, self-rebuilt
Full-time 100% electric boondocking (no propane, no genny) since 2015

https://www.livesmallridefree.com

[Mike90250]

Maybe, At some point, aging and wear & tear internally to the cell, damages something before the chemistry wears out. Happens to all cells, Pb-H2So4, NiFe, LFP.....

Lead acid has it down to a fine science, like there is a timer in your 48 month car battery, 51 months and it dies.

[Sunking]

Contrary to what you hear there is chemical reactions in Li batteries just like Pb batteries. If a Li battery were purely ion exchange they would last forever. Reality is the electrolyte they use is Organic, and as the electrolyte breaks down with age and usage clogs up the boundary layers.

[PNjunction]

I treated my GBS lifep04 batteries well when I purchased them back in 2011.

However, in early 2018, despite my constant pampering, and occasional hard-hitting exercise, I believe they just started to show their age, and performance dropped rapidly. So I don't know - 8 years maybe well before hitting the 2000 cycle mark?

That's just my experience with THIS set of cells. YMMV.

[Sojourner1]

I treated my GBS lifep04 batteries well when I purchased them back in 2011.

However, in early 2018, despite my constant pampering, and occasional hard-hitting exercise, I believe they just started to show their age, and performance dropped rapidly. So I don't know - 8 years maybe well before hitting the 2000 cycle mark?

That's just my experience with THIS set of cells. YMMV.

Was this the 100ah batteries you made into a portable pack? Could you guess on how often you actually used these or sat partially charged?

[PNjunction]

These were the small 40ah cells. I used them for a lot of stuff, so I didn't really try to do anything lab type.

I often pulled about .5C, or 20ah for long periods of time, then accompanied by relatively miniscule 1-2A consistent draws from my receivers and whatnot. I didn't do any real deep discharge, not held them at full charge all the time.

Idle periods at partial charge was such a blessing compared to lead-acid maintenance, that they put a lot of operational fun back into things. Just pick up and go.

So this was more or less casual use. But I knew going in that most batteries, especially LFP, if treated correctly one can face the proposition of aging taking more of a hit than cycle life!

One has to be realistic about the cycle life, otherwise you may pay through the nose for cycles that get thrown away due to age. I knew that going in.

My old sgt used to say "if you got 'em, smoke em!". Well, lets not smoke the batts, but some may miss the point that LFP isn't a perpetual storage machine.

[Sojourner1]

Thanks for the follow up.

I'm 29 months on my GBS 500ah bank (4s5p) fulltiming using 30% daily with occasional 70% dod and many psoc weeks when the weather isn't cooperating with solar. Roughly 850 cycles at 30-35%. Time will tell for longevity at this fractional c life.

[zamboni]

Thanks for the feedback. I realize there are a lot of variables but just getting a little anecdotal information is nice. If 8 years is the "calendar life" the ROI calculation for LFP is still very favorable. FLA will probably be superior in strictly financial terms for quite a long time to come but the other benefits (sustained operation at PSOC) are pretty awesome in a mobile RE application. I've only got 1.5 years on my pack so it will (hopefully) be a long time before I have my own results to look at.