100AH lithium battery holds MORE power than 100AH lead acid??

[Pete7]

I think the assumption that a 100Ah LFP holds more energy than a 100Ah LA is nonsense.

How much energy can be drawn from a LA battery? Fast discharge will be less, slowly more energy. This is why LA are rated at the 10 or 20 hour point, or longer hour if the retailer has stuck their own label on the case wants to get cute and appear to be selling better batteries. Discharge a battery over 20 hours and you get more than the 10 hour rate. You can see this on the spec sheets for better quality batteries like Trojan.

So what about LFP? Watch Will Prowse as he discharges LFP batteries quickly. Some are just under the rated power, some over. That is more about the cells used in the battery and the claims made by the retailer.

[Chotu]

Originally Posted by Pete7

I think the assumption that a 100Ah LFP holds more energy than a 100Ah LA is nonsense.

So prove it doesn’t. I proved it did.

I’ll get you started:

Watts = Volts x Amps

Start there and show us how it’s nonsense.

We are just taking about normal boat loads here, not hooking welders up. 5 amps. 10 amps

[Pete7]

Originally Posted by Chotu

So prove it doesn’t. I proved it did.

We are just taking about normal boat loads here, not hooking welders up. 5 amps. 10 amps

So am I, just the odd induction stove being used

Have a look at the image I posted. It shows that the total power varies hugely depending on the rate of discharge. LFP less so.

Pete

[Tupaia]

Originally Posted by sailingharry

Not true. Or, at least not universally true.
Very few if any LFP batteries are listed by Wh. They are universally listed by Ah. An EVE280k, for instance, is 280Ah.
The detailed manufacturers spec sheet for the EVE280k lists the capacity as 280Ah. No where on the spec sheet are Wh mentioned at all. There may be manufacturers that calculate that number, but that is not normally the rating.

https://www.18650batterystore.com/products/eve-lf280k

Maybe not all but the majority.


Sterling 1280Wh

https://sterling-power.com/cdn/shop/...g?v=1680518048


Renogy 1365Wh

https://cdn11.bigcommerce.com/s-nkm2...120635.jpg?c=2


Winston 1.2Kwh
https://shop.gwl.eu/LiFePO4-Battery-...ells.html#tab2


Energy density is also quoted in KWh/Kg

[CrispyCringle]

Originally Posted by Chotu

So prove it doesn’t. I proved it did.

I’ll get you started:

Watts = Volts x Amps

Start there and show us how it’s nonsense.

We are just taking about normal boat loads here, not hooking welders up. 5 amps. 10 amps

How does Watt=V x A prove that 100AH lithium battery holds MORE power than 100AH lead acid? Makes no sense. For one thing, they aren't the same units. You arent comparing the same thing.

[Stu Jackson]

Could it be helpful to go to the definition of ah?


From the Inverter Store website: (most other websites say pretty much the same thing - none of them use voltage at all)



What Are Amp Hours?First off, let’s define what an amp hour is. An amp hour, or Ah, is a measure of how much current one battery can provide over a defined period, which in this case is measured in hours. Depending on the size of the battery in question, amp hours can also be calculated in smaller units. For example, AA batteries usually gauge power in milli-amp hours or mAh.
Deep cycle batteries, which are designed with more robust battery plates and materials to handle frequent charge and discharge cycles, are measured in Ah, as well as with “C” ratings.
Simply put, a C rating is a battery’s capacity discharged over time. For example, a C8 rated battery will discharge its stored power over an eight-hour time frame, while a battery with a C20 rating will run for 20 hours before being completely discharged.

[Chotu]

Originally Posted by Stu Jackson

Could it be helpful to go to the definition of ah?


From the Inverter Store website: (most other websites say pretty much the same thing - none of them use voltage at all)



What Are Amp Hours?First off, let’s define what an amp hour is. An amp hour, or Ah, is a measure of how much current one battery can provide over a defined period, which in this case is measured in hours. Depending on the size of the battery in question, amp hours can also be calculated in smaller units. For example, AA batteries usually gauge power in milli-amp hours or mAh.
Deep cycle batteries, which are designed with more robust battery plates and materials to handle frequent charge and discharge cycles, are measured in Ah, as well as with “C” ratings.
Simply put, a C rating is a battery’s capacity discharged over time. For example, a C8 rated battery will discharge its stored power over an eight-hour time frame, while a battery with a C20 rating will run for 20 hours before being completely discharged.

Of COURSE they don't use voltage.

The definition of amp hours isn't in question. What you posted is accurate.

defining amp hours has nothing to do with the energy storage in the battery and that's what is so interesting here! for decades we have all been talking about batteries like the amp hour rating is some measure of the energy that is stored in the battery. It kind of is. But it’s not accurate. And that’s what I have kind of stumbled upon here.

we have had it wrong. Well, at least once lithium came out. There was no reason to distinguish this stuff in the past when they were only lead chemistries. They all behaved the same way. Now with new battery chemistries, this old way of equating AH capacity to energy storage is inaccurate. By 8% or so as calculated by Harry

Energy is watts. (it in terms of energy over time, kWh)

defining the energy stored in the battery requires a voltage too.

[Chotu]

Originally Posted by CrispyCringle

How does Watt=V x A prove that 100AH lithium battery holds MORE power than 100AH lead acid? Makes no sense. For one thing, they aren't the same units. You arent comparing the same thing.

I can’t teach you guys this stuff. You’re going to have to get it on your own.

It makes perfect sense. You just don’t understand it.

first of all, it holds more energy not more power.

Second, just look at the simple little tiny equation above. You posted it. It’s perfect. watts are the measure of energy. amps are constant over a 50% discharge. that only leaves volts as a variable. Lithium puts out over 13 V the entire time. Lead puts out less. So Lead puts less energy out for a 50% discharge. It’s not that hard to understand.

Now run the equation through time. A becomes a constant with a value of 50 for a 50% discharge of a 100AH battery. V is a variable that changes over time. For lithium it's more than 13 for all time. For lead it goes down into the 12's for most of the discharge.

Now multiply V (as it changes over time) times the A and you end up with different W's. Different watts. Different energy delivered during a 50AH discharge from lithium vs lead.

If you can’t understand what I just wrote, you’re not going to understand the concept at all. Or the math. It’s not even hard math. It’s like basic multiplication. Over time.

[HeywoodJ]

This is just not that complicated. An Ah is an Ah. It represents a current of one Ampere flowing for a period of one hour. It is a somewhat useful measurement with batteries (on which another recent thread expended far too many electrons).

The amount of energy represented by that Ah depends entirely on the voltage. One Amp, for one hour, at 24V is 24Wh. The same Ah at 12V is 12Wh.

Chotu is correct that the amount of usable energy in LFP for a given Ah is generally greater than the average energy in a LA Ah because the average voltage is higher. This is not magic, and doesn’t make a huge difference. The voltage curve of LFP is very flat (one of the things we all like about it), when you take energy out the biggest part comes out with a voltage of ~3.2V/cell or 12.8V (“12V” nominal system). There’s some energy that will come out at higher (and lower) voltages, but the bulk will come out between about 12.6 to 13.2V (around that 3.2V/cell). With LA the average V is much more dependent on SoC. If you are a 20% DoD user with return to “full” every cycle you actually probably withdraw closer to 13V, at least at low currents. A more typical user probably withdraws at 12.4 to 12.6V, and therefore LFP wins, but only by about 8% or so.

Whether or not you can do anything useful with that difference in energy depends on what you are using it to do.

[sailingharry]

Originally Posted by Tupaia

Maybe not all but the majority.


Sterling 1280Wh

https://sterling-power.com/cdn/shop/...g?v=1680518048
/Kg

That's an interesting twist.
All of the cells are only rated in Ah.
When Sterling (for example) combines cells that are rated in Ah, they label them in kWh.
It is worth noting that while the battery itself is labeled in kWh, they do not list them that way routinely on their website.
This is Sterling's website and they list all of their batteries only by Ah with no reference or mention of kWh.
https://sterling-power.com/products/lithium-batteries
I suspect that the core specification is Ah, and the kWh stamped on the battery is a derived specification.

[kmacdonald]

Originally Posted by tanglewood

Yes, I think so. I'm not sure what the rating conventions or standards are, or even if there are any, but in practice I agree that a 100Ah LFP battery will have more stored energy than a 100Ah lead battery. The stored energy would be expressed in Kwh.


I think there are 3 things that favor LFP:


1) A higher overall discharge voltage


2) A discharge voltage that drops much less over the SOC range.


3) Zero Peukert effect in the discharge current ranges that we care about.

IMHO the biggest benefits of lithium are charge efficiency and less weight and space savings.

[Stu Jackson]

This is a very succinct answer to the ? chotu originally raised. There is a difference between the 'difference in ah' (which is none) vs. the difference in energy. Thank you.

Originally Posted by HeywoodJ

This is just not that complicated. An Ah is an Ah. It represents a current of one Ampere flowing for a period of one hour. It is a somewhat useful measurement with batteries (on which another recent thread expended far too many electrons).

The amount of energy represented by that Ah depends entirely on the voltage. One Amp, for one hour, at 24V is 24Wh. The same Ah at 12V is 12Wh.

Chotu is correct that the amount of usable energy in LFP for a given Ah is generally greater than the average energy in a LA Ah because the average voltage is higher. This is not magic, and doesn’t make a huge difference. The voltage curve of LFP is very flat (one of the things we all like about it), when you take energy out the biggest part comes out with a voltage of ~3.2V/cell or 12.8V (“12V” nominal system). There’s some energy that will come out at higher (and lower) voltages, but the bulk will come out between about 12.6 to 13.2V (around that 3.2V/cell). With LA the average V is much more dependent on SoC. If you are a 20% DoD user with return to “full” every cycle you actually probably withdraw closer to 13V, at least at low currents. A more typical user probably withdraws at 12.4 to 12.6V, and therefore LFP wins, but only by about 8% or so.

Whether or not you can do anything useful with that difference in energy depends on what you are using it to do.

[Simi 60]

Originally Posted by Pete7

I think the assumption that a 100Ah LFP holds more energy than a 100Ah LA is nonsense.
.

Easily proven for us.

We had 880ah @ 24v in AGM
We could run our refrigeration, computers etc on that but once the batts got down around 50% things started changing for the worse rapidly
Voltage sag when one of the several 240v fridges kicked in was noticeable
Running things like a 1.8kw hot water system were immense loads and needed doing during the day with big solar to help or things would start shutting down as voltage under load dropped below 24v

Now we have 840ah of lifepo4
We have replaced the 1.8kw hot water with a 2.4kw model and it's now left on 24/7
Run air fryer, induction cooktop, electric kettle and and and as extras that we couldn't before on agm
Voltage sag is a thing of the past and we run the batts down to 30% before thinking about doing anything about it and even then, the voltage is still up around 26v
We get days extra from slightly less Ah batteries.

[SaylorMade]

Originally Posted by Tupaia

Maybe not all but the majority.


Sterling 1280Wh

https://sterling-power.com/cdn/shop/...g?v=1680518048


Renogy 1365Wh

https://cdn11.bigcommerce.com/s-nkm2...120635.jpg?c=2


Winston 1.2Kwh
https://shop.gwl.eu/LiFePO4-Battery-...ells.html#tab2


Energy density is also quoted in KWh/Kg

Litteraly every link you posted, has the Ah listed as well

[Tupaia]

Originally Posted by SaylorMade

Litteraly every link you posted, has the Ah listed as well

Well of course it does.
The point is that it is only possible to quote Wh for LPO because the voltage stays relatively constant during discharge 12v 100Ah = 12.8 x 100 = 1280Wh