Lithium discharge vs. AGM Discharge

[Russ]

I have read a bunch lately. I came across an article in the last couple days about battery discharge rates. It said an AGM battery can be discharged to about 75% to be safe. A lithium battery can be completely discharged or 20% to be safe. Does this mean that a 100 ah Lithium battery such as Battle Born or others will last twice as long as a AGM 100 ah before it needs recharging. This would mean that instead of me having solar power for example 5 hours on AGM I would have 10 hours of Solar power on Lithium before switching back to grid?

So if I have a AGM 100 ah it will last the same as a Lithium 50 ah of usable power before needing to be charged again?

The main advantage it seems I have heard over and over is that battery life is much longer and they cost a lot more.

Thanks in advance if you can help !

 

[Rider]

That's pretty much correct, except an AGM safe range is more like 50%. The big difference is that an AGM can supply loads more high power draw in a short time than lithium.

 

[svetz]

It's "safe" to take lead acid to any level of discharge... but the lower the depth of discharge (DoD), the fewer cycles you can get out of them.

Assuming it's a trustworthy vendor they'll have a table in their datasheet... something like the one below. Then for your application you can determine an appropriate depth of discharge for you. For example, if it's emergency use only and you'll use them 50 times in a decade, no reason not to take them down to 90% DoD.

 

[TCgreg]

With drop in lithium you should expect to get 100% of their advertised capacity. The extra 15-20% should be built in. In other words a Battleborn should exceed 100ah without its BMS moderating the total capacity but for margin of safety consumer will see just the 100Ah.

With led acid batteries any level of discharge is possible but as others mention the total number of lifecycles will diminish the deeper you dive. That isn't necessarily a bad thing. If you get 1000 cycles from 2 batteries at 50% dod or 600 cycles from one battery at 80% dod your scale of economy isn't as lopsided as people might think.

 

[Russ]

It's "safe" to take lead acid to any level of discharge... but the lower the depth of discharge (DoD), the fewer cycles you can get out of them.

Assuming it's a trustworthy vendor they'll have a table in their datasheet... something like the one below. Then for your application you can determine an appropriate depth of discharge for you. For example, if it's emergency use only and you'll use them 50 times in a decade, no reason not to take them down to 90% DoD.

So if it is not going to be used bt 50 times you are saying it can be discharged to only 10% of the charge left?

 

[Russ]

That's pretty much correct, except an AGM safe range is more like 50%. The big difference is that an AGM can supply loads more high power draw in a short time than lithium.

Never heard this. Can you expand on this or give an example? Sounds like you are saying it can handle a Surge of Power better than Lithium. An analogy I am thinking is like a generator may be 3000 watts but can handle a brief 3500 watts. Yes I know I said watts and not amps but this was just an analogy.

 

[Rider]

It's just the nature of the chemistry. If you look at a lead acid car battery, it has a rating for CCA (Cold Crank Amps). Lithium batteries don't have an equivalent because they just can't provide the extended high amp surge like lead acid.

I know it's been discussed here on this forum, just not sure where.

 

[Russ]

Ok so is this statement below correct?
If I have a AGM 100 ah it will last the same as a Lithium 50 ah of usable power before needing to be charged again? To not be so ambiguous can we say 50% discharge on both or 50% on the AGM and 25% on the Lithium.

I am just trying to determine if 2 VMax tank 100 ah AGM is about equal to one 100 ah Lithium batteries. If I am using 1000 or 1500 watts and a 100 ah AGM will keep everything running for 5 hours or however long, will a 100 ah Lithium keep everything up and running for 10 hours. Not easy for me to communicate this question guys

 

[Rider]

Ok so is this statement below correct?
If I have a AGM 100 ah it will last the same as a Lithium 50 ah of usable power before needing to be charged again? To not be so ambiguous can we say 50% discharge on both or 50% on the AGM and 25% on the Lithium.

Assuming a 50% discharge of the 100Ah AGM, a 50Ah Lithium can go down to about 10%, and have roughly the same total wattage output before recharging. In essence, a 100Ah lithium can provide nearly double the USABLE energy of a 100Ah lead acid.

 

[Russ]

It's just the nature of the chemistry. If you look at a lead acid car battery, it has a rating for CCA (Cold Crank Amps). Lithium batteries don't have an equivalent because they just can't provide the extended high amp surge like lead acid.

I know it's been discussed here on this forum, just not sure where.

Now I understAND THANKS !!!

 

[Russ]

Assuming a 50% discharge of the 100Ah AGM, a 50Ah Lithium can go down to about 10%, and have roughly the same total wattage output before recharging. In essence, a 100Ah lithium can provide nearly double the USABLE energy of a 100Ah lead acid.

That is what I was thinking. You answered it in the "elementary terms" that I can understand !!!!!
Learning fast on this site.

On the Explorist.Life website it is $40.00 a month for 1 on 1 support. I paid for one month a few days ago and I am learning much quicker here and from more than one point of view.

 

[b.james]

It's just the nature of the chemistry. If you look at a lead acid car battery, it has a rating for CCA (Cold Crank Amps). Lithium batteries don't have an equivalent because they just can't provide the extended high amp surge like lead acid.

I know it's been discussed here on this forum, just not sure where.

Mate thats just not right. LFP will deliver just as much current and at a higher voltage than lead acid. That means the amps will be less to produce the same punch as L/A. I can confirm that as I start my diesel pump with a 12 V 50Ah pack often . They are installying LFP in high end cars in Hong Kong. L/A suffers from needing to be quickly recharged to full straight away or it will die quickly. LFP does not . L/A is dead.

 

[svetz]

So if it is not going to be used but 50 times you are saying it can be discharged to only 10% of the charge left?

I'm saying check the manufactures datasheets. But overall sure! It's not a matter of personal or battery safety; it's about battery economics and longevity. A lead acid won't explode even if you drain it dry; all that draining it to a low depth of discharge does is to dramatically shorten it's possible life span. The reason you typically see 45 to 60% DoD for lead is that is usually where the best economics lie for the battery; but that might not be a good assumption for your usage. As members like @Deno have reported and from manufacturer datasheets you can see Lead can have a good number of cycles.

But the real impact of what I'm saying is understanding how many charge cycles you want out of a battery will enable you to understand the best DoD for you, and allow you to compare different batteries at different costs in an apples-to-apples way.

Let's work an example. Say you want to cycle a battery everyday for 10 years; you need 3,650 cycles. Battery A costs $68.50 and has 500 cycles at 65% DoD. Battery B costs $1,000 and has 10,000 cycles at 90% DoD. Which is right for you?

Assuming the full DoD everyday, you need about two As for one B. Since 10,000 > 3650 you'd only ever need 1 so buying battery B will cost $1000.
For Battery A, to get 3,650 cycles at the DoD you'd need 2x3650/500x$68.50 = $1000. So, in this case the price is the same.

As an exercise, which is better if Battery B gets 1000 cycles at 45% DoD? Which is better if you only need 50 cycles?

Other factors:

• The time value of money. One Battery A would last over a year, the money you didn't spend on Battery B can be making you money. Or, if you can't afford battery B, buying a Battery A now would hold you for a year so you could save up for it - and in that time Battery B's price might come down.
• In addition to cycles being greatly affected by DoD, the actual power from lead chemistry depends on the current draw rate and ambient temperature, see the Battery FAQ .
• Weight, lead acid batteries are heavier. Not much savings if you hurt your back or crack your floor.
• Battery maintenance/venting, FLAs in particular need a lot of care. (seriously, don't buy FLAs, don't even take them for free )
• Low Temperature operation
• Extra work in replacing more batteries (remember, they're heavy).
• You generally get cash back for turning in lead batteries, you might have to pay to dispose of lithium.

 

[eddie1261]

Let's work an example. Say you want to cycle a battery everyday for 10 years; you need 3,650 cycles. Battery A costs $68.50 and has 500 cycles at 65% DoD. Battery B costs $1,000 and has 10,000 cycles at 90% DoD. Which is right for you?

In concert with this post, find my post about "cheap vs inexpensive". You can probably buy a used lead acid battery from Bob's Battery Barn for $25. Yes, it will work. For a while. But if you keep going back to Bob for a series of used lead acid batteries, in 10 years you will have spent more than the $700-ish a lithium would have cost you. And that's the difference. Bob is cheap. Lithium is inexpensive. Cheap is about quality. Inexpensive is about price.

 

[svetz]

Yep, the math's only as good as the datasheet. Many countries do not have legally binding datasheets like the U.S.

 

[Bob B]

It's just the nature of the chemistry. If you look at a lead acid car battery, it has a rating for CCA (Cold Crank Amps). Lithium batteries don't have an equivalent because they just can't provide the extended high amp surge like lead acid.

I know it's been discussed here on this forum, just not sure where.

The factor that normally limits the current draw from a LiFePo4 is the BMS, not the battery cells. If you build your own, you can match the cell capabilities to the BMS ... or find an off the shelf with a higher current BMS.

 

[Russ]

Man you guys are awesome

 

[RandyP]

Yep, the math's only as good as the datasheet. Many countries do not have legally binding datasheets like the U.S.

Legally Binding Data sheets. More on this requirement please.

 

[svetz]

In the U.S. it's against the law for manufacturers to misrepresent their products. ref

 

[NakeDiesel]

So, while you guys are discussing agm vs lifepo4, I'm trying to figure out batteries for my water well. Normal op, no issue figuring that out. It's the startup amps. Plan on 48v battery bank and start surge will be around 227 amps on a 48v bank for a few seconds. Inverter will be an aims low freq inverter. Normal runtime will be about 10 min a day, with 3 days backup, 100ah will work for that. I think agm would be the better option, what are your thoughts?