Does battery weight matter?

Speedster said:
Firstly, the lithium option will last multiple times longer than the lead acid combination.
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The point was to factor this out by oversizing lead acid 1:4. Lead acid can live a long time but only if DoD < 25% or so, vs. lithium doing 80%+.

Speedster said:
Lithium also charges faster (which is important under high load shedding stages).
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I'm not sure this is true once you have the 4x oversizing of lead but I agree it may be a factor in some cases.

Speedster said:
Regarding your use of you car battery (which is pretty clever, by the way) that's a different argument to buying. Obviously using what one had is first prize, but if you were to buy a battery for that purpose a lithium one would get you a lot further for the same price.
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Even new I'm not so sure. It's a 15 W load. A new 576 Wh car battery is R 1300. Running it 2-4 hours, 5-10% DoD, I'd expect 5+ years, maybe 10. But I can also occasionally run it down 12+ hours. Even 24 hours is only 60% DoD which will not kill it dead if it's a rare thing. I'm arguing this is a useful feature of oversized lead acid. Meanwhile for LiPo today I could maybe get 13x 18650 @ 2.5 Ah = 120 Wh... I'd expect this to live 5 years too, but it couldn't ever help me out past 8 hours.
 
AchmatK said:
I like the Afrikaans saying, goedkoop is duur koop.

That 7Ah lead acid is not going to last a month of stage 6 load shedding.
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As you admitted, this is because the chargers in gate motors/alarms are insufficient, regardless of chemistry.

I'm seeing <100 mA in mine.

But still, if you are living in a place a couple of years, why invest in 10+ year tech for the next owner to enjoy?
 
Tomtomtom said:
Lead acid lifespan can be measured in years if used right. Key is to massively oversize vs lithium. Where 20 Ah lithium will do you might need 50+ Ah lead acid to get comparable cycle life.

If lead acid is still the cheaper option in a fair comparison go for it.
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And how many hours does your massively oversized battery take to charge?
 
Tomtomtom said:
The point was to factor this out by oversizing lead acid 1:4. Lead acid can live a long time but only if DoD &lt; 25% or so, vs. lithium doing 80%+.


I'm not sure this is true once you have the 4x oversizing of lead but I agree it may be a factor in some cases.



Even new I'm not so sure. It's a 15 W load. A new 576 Wh car battery is R 1300. Running it 2-4 hours, 5-10% DoD, I'd expect 5+ years, maybe 10. But I can also occasionally run it down 12+ hours. Even 24 hours is only 60% DoD which will not kill it dead if it's a rare thing. I'm arguing this is a useful feature of oversized lead acid. Meanwhile for LiPo today I could maybe get 13x 18650 @ 2.5 Ah = 120 Wh... I'd expect this to live 5 years too, but it couldn't ever help me out past 8 hours.
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Even if significantly oversized, you're getting way less out of LA than LiFePO4. A good LA will maybe give you 400 cycles. If you've oversized by a factor of 4 that's an equivalent of 1600 cycles if you really look after them well. LiFePO4s should comfortably give you in excess of 5000 cycles.

I really don't get why you're so set on advocating for LA when all the evidence shows they're a defunct technology (except for very short, high draw scenarios).
 
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Speedster said:
Even if significantly oversized, you're getting way less out of LA and LiFePO4. A good LA will maybe give you 400 cycles. If you've oversized by a factor of 4 that's an equivalent of 1600 cycles if you really look after them well. LiFePO4s should comfortably give you in excess of 5000 cycles.

I really don't get why you're so set on advocating for LA when all the evidence shows they're a defunct technology (except for very short, high draw scenarios).
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As in starter motors and not as a backup solution.
 
wingnut771 said:
And how many hours does your massively oversized battery take to charge?
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If I'm not mistaken I think LA should be charged low and slow at 0.025C which replenishes 50% of its rated capacity over a 20 hour period.

It's also the recommended discharge rate to be able to draw it down to 50% DOD over a 20 hour period.

Imagine the size of the LA battery bank if you have a constant load of 500w. That's over 20kwh. It can handle spikes but not anything constant or over any meaningful length of time.
 
wingnut771 said:
And how many hours does your massively oversized battery take to charge?
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About 1.5-2.5 times the outage duration. Here are some cycles from the last 24 hours - first one following a 4-hour session, and at the 2h mark the controller considers the battery full briefly before the current session.

vbatt.png

The noise is because the rate is temperature-limited and so only about 1 amp. We have a problem past stage 6 of course. I will make a call then. Lead acid has no problem absorbing charge, it takes time to equalise.

Speedster said:
Even if significantly oversized, you're getting way less out of LA and LiFePO4. A good LA will maybe give you 400 cycles. If you've oversized by a factor of 4 that's an equivalent of 1600 cycles if you really look after them well. LiFePO4s should comfortably give you in excess of 5000 cycles.
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My whole point is that there is some oversize factor where the cycle life is equal between the chemistries.

Cycle life versus DOD curve for a lead-acid battery


If I'm reading this correctly the crossover with your 5000 cycles is at about 15% DoD.
 
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Tomtomtom said:
About 1.5-2.5 times the outage duration. Here are some cycles from the last 24 hours - first one following a 4-hour session, and at the 2h mark the controller considers the battery full briefly before the current session.

View attachment 1444385

The noise is because the rate is temperature-limited and so only about 1 amp. We have a problem past stage 6 of course. I will make a call then. Lead acid has no problem absorbing charge, it takes time to equalise.



My whole point is that there is some oversize factor where the cycle life is equal between the chemistries.

Cycle life versus DOD curve for a lead-acid battery


If I'm reading this correctly the crossover with your 5000 cycles is at about 15% DoD.
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So now we're at oversizing by a factor of 6? Also, where'd you get that graph? I'm yet to see a LA battery that gives anywhere near 300 cycles at 100% DoD. I think you'd be lucky to get 30 cycles at that rate.
 
Speedster said:
I really don't get why you're so set on advocating for LA when all the evidence shows they're a defunct technology (except for very short, high draw scenarios).
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Because I'm a contrarian obviously.

But honestly I'm not advocating for LA in some blanket way. I've agreed it's on its way out (since 1859) and most scenarios today lithium is the hands-down better tech. Definitely if you're running your own power plant like @AchmatK.

OTOH most people here are arguing *against* LA in absolute terms. Lots of the interesting physical and economic complexity gets run over in the process.

Think why incandescent bulbs are still used in ovens. A similar thing applies to LA in certain circumstances. It's interesting to know what those might be.
 
Speedster said:
Even if significantly oversized, you're getting way less out of LA than LiFePO4. A good LA will maybe give you 400 cycles. If you've oversized by a factor of 4 that's an equivalent of 1600 cycles if you really look after them well. LiFePO4s should comfortably give you in excess of 5000 cycles.

I really don't get why you're so set on advocating for LA when all the evidence shows they're a defunct technology (except for very short, high draw scenarios).
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Is it really 5000 cycles?
I see a lot of adverts quote 3000, but I only recently learnt that they build them with second hand (2nd life) cells.
 
Tomtomtom said:
Because I'm a contrarian obviously.

But honestly I'm not advocating for LA in some blanket way. I've agreed it's on its way out (since 1859) and most scenarios today lithium is the hands-down better tech. Definitely if you're running your own power plant like @AchmatK.

OTOH most people here are arguing *against* LA in absolute terms. Lots of the interesting physical and economic complexity gets run over in the process.

Think why incandescent bulbs are still used in ovens. A similar thing applies to LA in certain circumstances. It's interesting to know what those might be.
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Incandescents are used in ovens and fireplaces because new tech can't handle the heat. The only place where LA still has any merit for consumers is in starting cars/bikes.
 
Tomtomtom said:
Just one other quick point about economic factors that favour making the "wrong" tech choice - say you have a gate motor or alarm system in a place you're only staying 2-3 years. Is there a lithium 7 Ah drop-in replacement that costs < R 300?
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As others have pointed out, you're saving money in the short term but it will cost you in the long term. Directly speaking to this example, we had lead acid batteries in our alarm. For stage 2 over a couple of days this was okay. The moment we went above stage 2, or had longer blocks of time with stage 2 active, we would be woken up in the middle of the night by the battery dying and the alarm going off. This happened several times over several years with various lead acid batteries.

I eventually got so gatvol about losing sleep that I spend R850 of a lithium ion replacement. I have not had a single issue with that thing even across regular stage 6. I went out and bought a spare to keep just in case. After multiple months of stage 2/4/6 I still have my original lithium ion battery in the alarm and it's been more than a year. I'd have likely gone through at least 4-6 lead acid batteries during the same period.

So 1 x R850 at the shop for LI (at the time, it's now R1000) vs 4-6x R250 for LA (being generous here, most walk-in places by me sell lead acid at R300-R350) R1000-R1500. So I saved R150 when I bought the battery, and I don't have to get up in the middle of the night to turn the alarm off and then struggle to get back to sleep.
 
zolly said:
As others have pointed out, you're saving money in the short term but it will cost you in the long term.
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Two points.

1. This doesn't answer my question about what to do if you're only in the house for a couple years. For many people talking 5-10+ years with these things is just irrelevant because they're not looking that long-term.

2. As @AchmatK has pointed out and I can attest to, the real problem is that gate motors/alarms etc. simply don't have fast enough chargers to tolerate < ~90% grid availability. Whatever your chemistry, you will run into trouble sooner or later at continuous stage 6+. I'm first putting in an external solar charger and then I'll look at lithium.
 
BuckRogers said:
Is it really 5000 cycles?
I see a lot of adverts quote 3000, but I only recently learnt that they build them with second hand (2nd life) cells.
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The pylontechs I have are rated for more than 6000 cycles at 95% DoD and the guys in Australia who did those long term tests showed that this is very feasible. If you go slightly lower on DoD that number goes up even higher. IIRC warranty on the ones I have is for 70% capacity after 7 years and 60% after 10 years.
 
Has anybody here run a lithium battery beyond the cycle life that put on the sticker? Do they just die ? Do they lose capacity?

Like hubble s-100A +- 4000cycles what happens after that?
 
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