# lead acid battery cost calculation



## chinabusiness (Feb 6, 2012)

Hey guys , 

Recently I was comparing the usage of LiFePo4 battery and lead acid battery used in solar system . I wanted to compare the cost .

I don't know much about lead acid battery , just now I communicated with a friend about the price calculation of lead acid , I found the following . 

Assuming that the unit price for LiFePo4 and lead acid was both : 1USD/AH 

For lead acid battery : 12V 100AH : 1USD*100AH 
24V 100AH : 1USD*100AH*2 PCS


For LiFePo4 : 12V 100AH : 1USD*100AH*4PCS (of single cells) 24V 100AH : 1USD*100AH*8 PCS( of single cells)

My friend said for lead acid battery , the nominal voltage for single cells is 12V in price calculation . Isn't the lead acid single cell nominal voltage is 2.0V ? 

That is not fair .... Even if the unit price was the same , LiFePo4 pack cost will always be 4 times of lead acid's ... of course the unit price is definitely not the same . LiFePo4's is higher . 

I thought it was 2V nominal voltage for lead acid cell . There is 6V lead acid battery , yes ? 

Please don't laugh at me but I thoght it should be : 12V 100AH lead acid: 1USD*100AH*6PCS ...


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## frodus (Apr 12, 2008)

True, the cell voltage in a Lead Acid battery is 2V, but there's 6 cells in 12V batteries, 3 cells in 6V and 4 cells in 8V.

Normally they're sold as groups of 6V, 8V or 12V (and 24V sometimes) for lead acid.


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## chinabusiness (Feb 6, 2012)

frodus said:


> True, the cell voltage in a Lead Acid battery is 2V, but there's 6 cells in 12V batteries, 3 cells in 6V and 4 cells in 8V.
> 
> Normally they're sold as groups of 6V, 8V or 12V (and 24V sometimes) for lead acid.


 
Thanks for reply . 

The key point is when calculate the price , 12V is used as a single cell voltage . 

For example , 6V 100AH and 12V 100ah lead acid battery pack - how to calculate their price ? Eg, unit price : 1USD/AH 

Or the unit price for lead acid is actually calculated as per wh ...


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## Ziggythewiz (May 16, 2010)

No, 12V is used as a single BATTERY voltage. No one calls a 12V battery a cell because it has 6 cells. You can call a cell a battery but you can't call a 12V battery a cell.

$/ah is not used to calculate the price of lead batteries in general, only lithium. If you are trying to decide between 1 6v and another (just as lithium to lithium is typically 3.2) it's fine to use $/ah, but if you're comparing 6V and 12V it doesn't make any sense. A 6V will always have the better $/ah value.

Better would be to compare 

total lifetime $/kWh = PackVoltage/UnitVoltage*UnitCost/(kWh/cycle*cyclelife)


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## chinabusiness (Feb 6, 2012)

Ziggythewiz said:


> No, 12V is used as a single BATTERY voltage. No one calls a 12V battery a cell because it has 6 cells. You can call a cell a battery but you can't call a 12V battery a cell.
> 
> $/ah is not used to calculate the price of lead batteries in general, only lithium. If you are trying to decide between 1 6v and another (just as lithium to lithium is typically 3.2) it's fine to use $/ah, but if you're comparing 6V and 12V it doesn't make any sense. A 6V will always have the better $/ah value.
> 
> ...


 
Thanks very much for the reply . 

I think I got the point . Can regard 12V as a unit ( and people usually regard 12V as a unit in lead acid battery industry) .If we use $/AH , then unit price times Ah will be the (12V) unit cost . 

Then any pack cost will be : pack voltage/12V *unit cost .

I was just confused how people calculate price in lead acid battery buy and sell . 

When I talked with a customer who never used lithium battery before ... 
I calculate 12V 100ah pack :$/ah*100ah* 4 pcs - he asked me why you times 4 ?? 

He said for lead acid battery 12V 100ah, just $/ah*100ah 

And I happen to know little about lead acid , which made me think about all above ... 

Maybe I should say 12V as a unit is a standard in lead acid battery industry .

Thanks very much for help .


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## frodus (Apr 12, 2008)

If you want to compare between chemistries, you need to use $ per Wh if you really want to compare them.

you know the Wh in both, right? amp-hours x volts = Wh. You know Cost/Wh = Dollars per watt hour.

So if a CALB 100Ah cell is $125, and a AGM 55Ah Optima D34 battery is $249....

100Ah x 3.2V = 320Wh, and $125/320Wh is $0.39/Wh.
55Ah x 12V = 660Wh, and $249/660 is $0.38/wh


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## Ziggythewiz (May 16, 2010)

chinabusiness said:


> Maybe I should say 12V as a unit is a standard in lead acid battery industry .


I wouldn't say that at all, that's true of the car battery industry, but for other applications there are quite a few 6V, 8V, and 24V lead batteries out there as well.

As frodus shows, there's the up front cost to consider, but there's more to it than the sticker numbers. You also need to consider peukert and safe DOD.

Here's some examples of some cheaper lead acids compared to lithium: (I worked these with EV in mind, for solar the peukert would be less significant, so you could probably replace those with .9 and bring the lead costs down by 30-40%)

Cost/Wh = UnitCost/(AH * SafeDOD * peukert * UnitVoltage)
TotalCost = PackVoltage/UnitVoltage*UnitCost
LifeCost/kWh = TotalCost/(AH * SafeDOD * peukert * PackVoltage * cycles) * 1000

12V 29DC:
Cost/Wh = $94/(125*.5*.5*12) = $0.25/wH
TotalCost = 120/12*94 = $940
LifeCost/kWh = $940/(125*.5*.5*120*300) * 1000 = $0.84/kWh

8V EGC:
Cost/Wh = $91/(135*.5*.63*8) = $0.27/wH
TotalCost = 120/8*91 = $1365
LifeCost/kWh = $1365/(135*.5*.63*120*500) * 1000 = $0.53/kWh

6V EGC:
Cost/Wh = $81/(225*.5*.57*6) = $0.21/wH
TotalCost = 120/6*81 = $1620
LifeCost/kWh = $1620/(225*.5*.57*120*700) * 1000 = $0.30/kWh

LiFePO4:
Cost/Wh = $125/(100*.8*1*3.2) = $0.49/wH
TotalCost = 120/3.2*125= $4688
LifeCost/kWh = $4688/(100*.8*1*120*2000) * 1000 = $0.24/kWh

**Disclaimer - most values based on published specs; some are estimates or worse


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## chinabusiness (Feb 6, 2012)

frodus said:


> If you want to compare between chemistries, you need to use $ per Wh if you really want to compare them.
> 
> you know the Wh in both, right? amp-hours x volts = Wh. You know Cost/Wh = Dollars per watt hour.
> 
> ...


Yes , thank you very much really . 

I think it makes great sense to use cost/wh to compare different chemistry battery .


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## chinabusiness (Feb 6, 2012)

Ziggythewiz said:


> I wouldn't say that at all, that's true of the car battery industry, but for other applications there are quite a few 6V, 8V, and 24V lead batteries out there as well.
> 
> As frodus shows, there's the up front cost to consider, but there's more to it than the sticker numbers. You also need to consider peukert and safe DOD.
> 
> ...


Thanks very much for the above really . I took nearly 2 hours to digest this . 

Previously I just knew lead acid capacity is usually calculated as per 20 hour rate and higher current , less capacity . I didn't know the term Perkurt . 

by googling , I found the following :

*The capacity at a one-ampere discharge rate is not usually given for practical cells. It is useful to reformulate the law to a known capacity and discharge rate:*
*where:*
*is the rated discharge time, in (hours). is the rated capacity at that discharge rate, in (**Ampere-hours**). is the actual discharge current, in (Amps). is the Peukert constant, (**dimensionless**). is the actual time to discharge the battery, in (hours). Using the above example, if the battery has a Peukert constant of 1.2 and it is discharged at a rate of 10 amperes, it would be fully discharged in time which is approximately 8.7 hours. It would therefore dispense only 87 ampere hours rather than 100.*
*Peukert's law can be written as:*
*giving which is the effective capacity at the discharge rate .*

*when I post , the equation/formula can't be shown : Link is here :**http://en.wikipedia.org/wiki/Peukert's_law*


From the above we can see H (rated discharge time) is 20 - that is 20 hour rate . 

But by observing several lead acid battery specification . For example a 12V 200AH battery ,it has the following :
20 hour rate :208 ah 
10 hour rate :200ah 
5 hour rate : 185ah
1hour rate : 110AH




The capacity they quoted is 10 hour rate .


And another 12V 110AH gel battery , it has the following specs:

20 hour rate :126AH
10 hour rate :120AH

5 hour rate :102AH

1 hour rate :66AH



Then it 110Ah should be about 6 hour rate . 


So I am thinking usually what hour rate capacity do people quote . 




Come to my original question - 

Or Could I say that :

Usualy the general lead acid unit pack is 6V , 8v ,12V .When the sellers quote , they usually quote in this way : how much is the 6V 8V or 12V pack .

As for how does the cost come ,that is not our problem and different suppliers might also have different price . 

Anyway , thanks very much . I learned much here .


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## Ziggythewiz (May 16, 2010)

Most sticker capacities for lead are at the 20 hour rate, if it's something else they will likely tell you (they don't want their 5 hr rate compared to someone else's 20 hr rate. 

For a solar application a 10hr rate is probably most appropriate. 

For EVs you want a 1 hr or possibly even a 1/2 hr rate, which will not exist if it isn't a battery designed for EV. For example, the EGC8s and EGC2s above have published 20, 10, 5, and 2 hr rates, but you have to estimate to turn that into a 1hr rate.

Most sellers would probably only be quoting a unit price and a volume unit price, not a pack price unless it's a standard pack size such as for a golf cart.


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## chinabusiness (Feb 6, 2012)

Ziggythewiz said:


> Most sticker capacities for lead are at the 20 hour rate, if it's something else they will likely tell you (they don't want their 5 hr rate compared to someone else's 20 hr rate.
> 
> For a solar application a 10hr rate is probably most appropriate.
> 
> ...


Thanks very much really for the explanation .

After talking all these above , I assume lead unit price is $/wh...


Thanks very much again for your time .


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## Ziggythewiz (May 16, 2010)

No, the lead unit price will be the price for a battery. You have to calculate the $/wh based on the voltage and provided capacity numbers, with peukert and safe discharge amounts in mind.


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## chinabusiness (Feb 6, 2012)

Ziggythewiz said:


> No, the lead unit price will be the price for a battery. You have to calculate the $/wh based on the voltage and provided capacity numbers, with peukert and safe discharge amounts in mind.


OK , I get it . Thanks very much .


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## MN Driver (Sep 29, 2009)

"Most sticker capacities for lead are at the 20 hour rate, if it's something else they will likely tell you (they don't want their 5 hr rate compared to someone else's 20 hr rate."

Except for the WalMart "125Ah" marine batteries that are rated at 1 amp. No joke, they are rated at 1/125C. Not to mention people here who have used them and barely got any use out of them.


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## Ziggythewiz (May 16, 2010)

MN Driver said:


> Except for the WalMart "125Ah" marine batteries that are rated at 1 amp. No joke, they are rated at 1/125C. Not to mention people here who have used them and barely got any use out of them.


Pretty sure that's a 20 hr rate, they can give over 50% of the rating in an EV when new. Where they crap out is in low cycle life.


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## MN Driver (Sep 29, 2009)

No, I was just there and saw it. The WalMart marine 'deep cycle' batteries specifically say 125Ah at 1 amp.


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## Ziggythewiz (May 16, 2010)

I didn't realize they still carried those anywhere. Here they pulled em from Wallmart (equivalent still at Sams 29HM) a few years ago, around the time they cancelled any warranties over 90 days (still do prorates)


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