Portable Power Stations

[Love Me Tender]

As far as I understand it, a cycle is not based on a charge.

Cool thanks, that definitely will give batteries a longer life span.

 

[Mirai]

As far as I understand it, a cycle is not based on a charge.

I understood it as say if you have a 100% charged battery and you drop it to 50%-- that's half of a cycle - then charge it by 25% and drop it by 50% again to 25% total capacity you've used 100% but your battery is still 25% full at that stage. You've now used 1 cycle.

So a good Li NCM will give you about 800-1000 cycles, so you can do that 799-999 more times or so.
For LiFePO you can do that about 2999 times more or so.

 

[Dan C]

I understood it as say if you have a 100% charged battery and you drop it to 50%-- that's half of a cycle - then charge it by 25% and drop it by 50% again to 25% total capacity you've used 100% but your battery is still 25% full at that stage. You've now used 1 cycle.

So a good Li NCM will give you about 800-1000 cycles, so you can do that 799-999 more times or so.
For LiFePO you can do that about 2999 times more or so.

Yip, a LifePo will last me 15 years

 

[Bundu]

I understood it as say if you have a 100% charged battery and you drop it to 50%-- that's half of a cycle - then charge it by 25% and drop it by 50% again to 25% total capacity you've used 100% but your battery is still 25% full at that stage. You've now used 1 cycle.

So a good Li NCM will give you about 800-1000 cycles, so you can do that 799-999 more times or so.
For LiFePO you can do that about 2999 times more or so.

AFAIK at the end of those cycles, your battery capacity is still 80% when fully charged

 

[Love Me Tender]

How would one interpret this battery cycles?

Cycle Life @ 1C: +/-1000 Cycles @ 100% DOD, Above 2000 cycles @ 80% DOD

Full Specs:
Nenergy 12.8V 100Ah LiFePo4 Single Battery Module
•Wall Mount Installation Unit
•Nominal Voltage: 12.8V
•Working Voltage Range 12V
•Rated Capacity 100Ah
•Total Usable Energy 1.280 kWh
•Maximum Continuous Charging Current: 20A
•Maximum Continuous Discharging Current: 50A
•Working Voltage Range 116V-14.6V
•Built In Protection -Over-Charge, Over-Discharge, Over-Temperature

 

[Tomtomtom]

It's not linear. You can't just add two 100->50% discharges and call it a cycle. They'll count for less than a single 100->0% cycle, by some amount that is not straightforward to calculate.

Avoiding the extremes is even better. So if you only do 80->30% then you can expect the cells to well exceed double the rated 100->0% cycle life. Maybe triple or more.

 

[Love Me Tender]

I am trying to figure out how the 1C affects the cycles

My understanding is 1C means it can be charged at full capacity - in this case 100A.
However the battery specs say it can only accept 20A max - which is 0.2C

Does this mean the battery could in theory do 5000 cycles at 100% DOD and 10000 cycles at 80% DOD using the 0.2C (20A of the 100A)

"1C: +/-1000 Cycles @ 100% DOD, Above 2000 cycles @ 80% DOD"

 

[Mirai]

It's not linear. You can't just add two 100->50% discharges and call it a cycle. They'll count for less than a single 100->0% cycle, by some amount that is not straightforward to calculate.

Avoiding the extremes is even better. So if you only do 80->30% then you can expect the cells to well exceed double the rated 100->0% cycle life. Maybe triple or more.

You are correct. That's not entirely linear but what would we use? Logistic regression?
If you discharge battery close to zero, how close is close to zero? Bluetti NCM claim 90% discharge rate is the lower limit for NCM and they claim a 1000 cycles.

If you strain the battery to let it go 100% DOD you will not get 3,000 cycles on LFP. Hence you should avoid the extremes. But if Bluetti claim 1000 cycles on Li NCM with a hard cut off at 90% DOD maybe the figures for LFP are conservative.

 

[Mirai]

Blue Nova 8AH battery:

Cycle Life @ 100% DoD > 2000 cycles (104 Wh @C10, 25°C) Cycle Life @ 80% DoD > 3000 cycles (83 Wh @C10, 25°C) Cycle Life @ 50% DoD > 5000 cycles (52 Wh @C10, 25°C

The question arises, how is the cycle counted? Is the 5000 cycles with 50% DOD counted as going 100% to 50% and recharging 5,000 times? Or is that half a cycle? Or can you do more cycles than 5,000 if you say oscillate between say 90% SOC and 60% SOC? If you go from 90% to 60%, 3 times is that a full cycle? Is that then part of the 5000?

 

[Tomtomtom]

The question arises, how is the cycle counted? Is the 5000 cycles with 50% DOD counted as going 100% to 50% and recharging 5,000 times?

Yes. In these ratings a cycle is one discharge to specified DoD followed by a full charge.

 

[Mirai]

Yes. In these ratings a cycle is one discharge to specified DoD followed by a full charge.

Thanks. So these take into account 100% charge state as well.

There's a lot of fear mongering about keeping batteries charged less at say 80%.

Probably a better metric would be to know the total lifetime output in watts of the battery depending on DOD.

 

[Tomtomtom]

There's a lot of fear mongering about keeping batteries charged less at say 80%.

It can make a big difference. e.g. here the light and dark blue lines represent the same energy extracted but look at the trajectories. Light blue heading for well over 10k cycles to 80%. It's a very easy way to extend lifespan. But obviously you lose the long runtime "option".



Plenty more at good old battery university including to your point about maximising lifetime energy.

 

[Mirai]

It can make a big difference. e.g. here the light and dark blue lines represent the same energy extracted but look at the trajectories. Light blue heading for well over 10k cycles to 80%. It's a very cheap way to extend lifespan.

View attachment 1515195

Plenty more at good old battery university including to your point about maximising lifetime energy.

Not really. Every Wh costs. So while you can over provision this allows you to work with bigger reserves each side of the spectrum you need to spend more upfront.

Look also at the top line, you can see that the cycles are high but each cycle is going from 75 to 65% capacity which is only 10% of the battery capacity = one cycle, so no wonder 8.500 cycles. The battery retains >90% capacity over 8.500 cycles but you never use that capacity.

 

[Tomtomtom]

Not really. Every Wh costs. So while you can over provision this allows you to work with bigger reserves each side of the spectrum you need to spend more upfront.

I edited "cheap" to "easy" a minute after posting Ja, this is the cost.

But I think it's fair to say that overprovisioning "pays" by returning disproportionately longer service life. (Or the corollary that everyone with lead acid runs into: under provisioning is expensive.)

That compounds also with the fact that "80% original capacity" isn't the relevant cutoff in practice vs making it through X hours.

 

[Mirai]

I edited "cheap" to "easy" a minute after posting Ja, this is the cost.

But I think it's fair to say that overprovisioning "pays" by returning disproportionately longer service life. (Or the corollary that everyone with lead acid runs into: under provisioning is expensive.)

That compounds also with the fact that "80% original capacity" isn't the relevant cutoff in practice vs making it through X hours.

Does it return a disproportionately longer battery life? If one overinvested in Li NMC they'd lose out now on LFP And batteries may get cheaper in the long run as more competitors come on the market.

Lead has more drawbacks though. It has the memory effect for one. It also charges slowly.

 

[Tomtomtom]

Does it return a disproportionately longer battery life?

Yes per the above non-linear lifespan dependency on cycle DoD. It's way worse for LA but all the chemistries seem to exhibit it.

I agree it's a tricky calculation taking opportunity cost and discount rates etc. into account but I wonder if people are too quick to say "100 W * 4 hours = 400 Wh required" when they might be better off going for say 1 kWh.

Especially for anything other than LFP!

But maybe I'm just justifying my own overprovisioning.

 

[KOPITE]

Yeah it's not bad. And I have 2 that are rated for 800 cycles to 80% capacity but if I buy another, it will have LFP instead of NMC.

Not just for the cycles, its also safer.

So after 800 cycles you still have 80% usage of the battery. that means it will last you 5-10 years depending on usage. the new LFP will probably last 20 years depending on usage and looked after.

I dunno why the big fuss of life time expectancy where it will last you a very long time

 

[Mirai]

So after 800 cycles you still have 80% usage of the battery. that means it will last you 5-10 years depending on usage. the new LFP will probably last 20 years depending on usage and looked after.

I dunno why the big fuss of life time expectancy where it will last you a very long time

These are expensive devices, so you want 3,000 cycles and the safety, I suppose. For me their attempt at pushing the Delta Max battery with the Delta 2 because they don't have a Delta 2 Max battery out yet is slimy. They don't have a disclaimer saying that battery is older tech.

 

[Tomtomtom]

So after 800 cycles you still have 80% usage of the battery. that means it will last you 5-10 years depending on usage.

Or it could last only months.

Back to the fact that "80% original capacity" isn't the relevant cutoff in practice vs making it through X hours. If you need 4 hours, and a new device gives you 5 hours with your load, then by the time it's got 80% capacity, the device is at the end of its useful life (for your purpose).

Also, you won't get the full 800 cycles, because your DoD was only 80% (the rating condition) on the first cycle. By the time you're only getting 4 hours, you are cycling at 100% DoD.

Then on top of that, degredation isn't linear even for costant DoD. There is a "knee" phenomenon where the battery rapidly falls apart.

So... overprovision, i.e. don't actually use the thing, and sure it could last years.

 

[Mirai]

Or it could last only months.

Back to the fact that "80% original capacity" isn't the relevant cutoff in practice vs making it through X hours. If you need 4 hours, and a new device gives you 5 hours with your load, then by the time it's got 80% capacity, the device is at the end of its useful life (for your purpose).

Also, you won't get the full 800 cycles, because your DoD was only 80% (the rating condition) on the first cycle. By the time you're only getting 4 hours, you are cycling at 100% DoD.

Then on top of that, degredation isn't linear even for costant DoD. There is a "knee" phenomenon where the battery rapidly falls apart.

So... overprovision, i.e. don't actually use the thing, and sure it could last years.

That's the scenario here. We have the Delta 2 for one laptop and another Bluetti NCM 500Wh unit for a second laptop (lower power draw one). Don't power anything else with that.

I sure as heck wouldn't boil water, use an induction cooker or toaster.