Lithium batteries - true longitudinal capacity profiles?

[booster]

Originally Posted by W9TR

This is good info, thanks all for posting. I wonder how more recently manufactured LiPO4 batteries will fare.

I’ll note that the 50% AGM discharge limit doesn’t hold up factually, at least for the Trojan 31 series AGM batteries in our van.

Trojan states that 50% DOD gets you 1000 cycles while 80% DOD gets you 600 cycles, seemingly a big lifecycle drop. But that’s not taking into account the extra energy you get by discharging to 20%.

For a 100 AH battery :
50% DOD gets you 50 AH x 1000 cycles = 50,000 AH lifetime.
80% SOD gets you 80 AH x 600 cycles = 48,000 AH lifetime.

So while I wait for my AGM’s to reach the end of their useful life (maybe longer than we own the van) I’ll discharge them to 20% when the need arises secure in the knowledge that I am doing no harm.

You might want to read some older threads on this forum about the 50% rule as they discuss exactly what you are talking about with a lot of data and detail. Bottom line when you calc it all out is that you get 60% more usable capacity (20-100% instead

instead of 50-100% SOC) and only lose 10-20% of total lifetime recoverable amp hours by going to 20% SOC.


Lithium also lists cycle life as number of recharge cycles, so the misunderstanding for them is the same thing. Per the latest information, lithium may even suffer more from deep discharges than lead acid, contrary to the early claims of the same life even at 100% discharge cycles.

[RossWilliams]

Originally Posted by W9TR

I’ll note that the 50% AGM discharge limit doesn’t hold up factually, at least for the Trojan 31 series AGM batteries in our van.

Trojan states that 50% DOD gets you 1000 cycles while 80% DOD gets you 600 cycles, seemingly a big lifecycle drop. But that’s not taking into account the extra energy you get by discharging to 20%.

For a 100 AH battery :
50% DOD gets you 50 AH x 1000 cycles = 50,000 AH lifetime.
80% SOD gets you 80 AH x 600 cycles = 48,000 AH lifetime.

So while I wait for my AGM’s to reach the end of their useful life (maybe longer than we own the van) I’ll discharge them to 20% when the need arises secure in the knowledge that I am doing no harm.

This is exactly what I was suggesting is a problem with company projections. While the math is correct, it is correct only if you are always discharging from a fully charged battery to 50% or 80% This is not how any of us actually use our batteries.

If "cycle" is defined as the equivalent of a full discharge then the math is 1,000,000 AH lifetime to 50% vs 600,000 AH to 80%, a 2/3 increase in energy by limiting the discharge level to 50%. If "cycle" really means every time you discharge and recharge then if you start at 60% charged you get only 10,000 AH if you discharge to 50%. You get 24,000 if you discharge to 80%, almost 2 1/2 times as much energy. In fact, all of those numbers are entirely theoretical. None of those calculations are likely to accurately reflect the real life span of your battery.

That said, my conclusion is much the same as yours. Operating with a floor of 50% will extend the life of your battery, but occasionally dropping below that is not going to have a significant impact. But generally the earlier you recharge the better. If I had a generator or access to shore power I wouldn't wait until it got to 80% discharged before recharging. And I wouldn't size my battery bank to need to regularly discharge to 80%.

Unless of course I was going to only own it for a couple years anyway. Then I might not pay too close attention to battery life.

[Billinnc]

@Interblog:"My gasoline-only Toyota Sienna is now 12 years old with 135,000 miles on it, and I’ve been weighing when to buy a new one, having almost pulled the trigger a couple of times recently. But all Siennas are hybrids at this point, and there is NO WAY I am going to purchase ANY car with LiFePO4 components until I have a much better understanding of this emerging situation."

For over twenty years Toyota has stuck with nickel metal hydride batteries for their non-plugin hybrids, including the 2023 Sienna hybrid. So a pretty good track record exists if that is a model you are interested in.

[MsNomer]

Originally Posted by W9TR

I’ll note that the 50% AGM discharge limit doesn’t hold up factually, at least for the Trojan 31 series AGM batteries in our van.

Trojan states that 50% DOD gets you 1000 cycles while 80% DOD gets you 600 cycles, seemingly a big lifecycle drop. But that’s not taking into account the extra energy you get by discharging to 20%.

For a 100 AH battery :
50% DOD gets you 50 AH x 1000 cycles = 50,000 AH lifetime.
80% SOD gets you 80 AH x 600 cycles = 48,000 AH lifetime.

So while I wait for my AGM’s to reach the end of their useful life (maybe longer than we own the van) I’ll discharge them to 20% when the need arises secure in the knowledge that I am doing no harm.

We bought into this and were perfectly willing to take our AGMs down to 20% or so until we realized that even Lifelines couldn’t run our microwave below about 75% SOC because of the voltage drop. So if you're thinking of running AGM to a low SOC, don't plan on any high-draw, or even moderately high-draw appliances. This is what drove us to lithium.

[avanti]

Originally Posted by MsNomer

So if you're thinking of running AGM to a low SOC, don't plan on any high-draw, or even moderately high-draw appliances.

...or have enough AGMs capacity to handle the load. Our Legend had 440Ah of AGM and we never had a low-voltage problem under any reasonable conditions.

[RossWilliams]

Originally Posted by MsNomer

We bought into this and were perfectly willing to take our AGMs down to 20% or so until we realized that even Lifelines couldn’t run our microwave below about 75% SOC because of the voltage drop. So if you're thinking of running AGM to a low SOC, don't plan on any high-draw, or even moderately high-draw appliances. This is what drove us to lithium.

I think the size of the voltage drop under load depends on the size of your battery bank. We have 8 AGM batteries and haven't seen that problem. Our voltage under load rarely drops below 12 volts.

But its another reminder that the energy in batteries doesn't work like fuel in the tank.

[booster]

Originally Posted by RossWilliams

I think the size of the voltage drop under load depends on the size of your battery bank. We have 8 AGM batteries and haven't seen that problem. Our voltage under load rarely drops below 12 volts.

But its another reminder that the energy in batteries doesn't work like fuel in the tank.

This relates to the lithium originals claims about very little voltage sag and it does appear to be much better with them over AGM.


Perhaps this AGM discussion should be on it's own as it is cluttering up Interblog's original topic a bit and we haven't yet heard what she plans on doing to make her next lithium batteries last longer.

[Davydd]

Originally Posted by RossWilliams

I think the takeaways apply to RV batteries in general. Manufacturers provide theoretical numbers based on hypothetical situations. Real life is going to be different. Battery life cycle and AH ratings are clear examples of this. They are useful for comparison, but not really for real world use.

Sizing your system substantially larger than the expected need is desirable if you are looking at permanent long term use. Perhaps not if you anticipate selling the RV long before it wears out. Early adopters of technology are always going to find that information on long term considerations was not available. That's part of being a "beta tester."

The same applies to new uses of old technology. The increased use of electricity rather than propane may have some long term effects on battery capacity in general. Relying on batteries to boondock running a microwave, stovetop, refrigerator, air conditioner and media center is a relatively new phenomena. So we don't really know.

It is helpful to recognize that cost and other comparisons of lithium to lead acid batteries are still relying on limited real world experience.

Damn! I didn't realize I was a beta tester for 9 years. I wonder how many word jockeys expounding on something they've never experienced keep it up. They don't know for sure. I think I do from experience and pleasurable one at that.

There are some companies that take their lithium batteries seriously and track every customer's use of lithium batteries. This is what Advanced RV does...

https://www.youtube.com/watch?v=zZg-buBMw-o&t=28s

[booster]

Originally Posted by Davydd

Damn! I didn't realize I was a beta tester for 9 years. I wonder how many word jockeys expounding on something they've never experienced keep it up. They don't know for sure. I think I do from experience and pleasurable one at that.

There are some companies that take their lithium batteries seriously and track every customer's use of lithium batteries. This is what Advanced RV does...

Did they ever tell you how much capacity your old van lost of the years?

[W9TR]

Originally Posted by RossWilliams

This is exactly what I was suggesting is a problem with company projections. While the math is correct, it is correct only if you are always discharging from a fully charged battery to 50% or 80% This is not how any of us actually use our batteries.

If "cycle" is defined as the equivalent of a full discharge then the math is 1,000,000 AH lifetime to 50% vs 600,000 AH to 80%, a 2/3 increase in energy by limiting the discharge level to 50%. If "cycle" really means every time you discharge and recharge then if you start at 60% charged you get only 10,000 AH if you discharge to 50%. You get 24,000 if you discharge to 80%, almost 2 1/2 times as much energy. In fact, all of those numbers are entirely theoretical. None of those calculations are likely to accurately reflect the real life span of your battery.

That said, my conclusion is much the same as yours. Operating with a floor of 50% will extend the life of your battery, but occasionally dropping below that is not going to have a significant impact. But generally the earlier you recharge the better. If I had a generator or access to shore power I wouldn't wait until it got to 80% discharged before recharging. And I wouldn't size my battery bank to need to regularly discharge to 80%.

Unless of course I was going to only own it for a couple years anyway. Then I might not pay too close attention to battery life.

Trojan defines a cycle from 0% DOD or fully charged, down to xx% DOD.
1000 cycles from 0% DOD to 50% DOD.
600 cycles from 0% DOD to 80% DOD.
So the math in my original post applies.
This is from Trojan’s AGM application guide.
Lots of other variables here like how long the battereis remain discharged, etc.

[W9TR]

Originally Posted by MsNomer

We bought into this and were perfectly willing to take our AGMs down to 20% or so until we realized that even Lifelines couldn’t run our microwave below about 75% SOC because of the voltage drop. So if you're thinking of running AGM to a low SOC, don't plan on any high-draw, or even moderately high-draw appliances. This is what drove us to lithium.

This is absolutely true - AGM’s have higher internal resistance than LiPO4 batteries so may not work under high current loads. We lose about 0.25V @ 1000 Watts load on our 200 AH AGM pack. That’s is OK for us because our biggest load is a 600 Watt coffee maker, which works fine right down to 80% DOD. I expect the voltage drop will increase as the batteries age.

[booster]

Originally Posted by W9TR

Trojan defines a cycle from 0% DOD or fully charged, down to xx% DOD.
1000 cycles from 0% DOD to 50% DOD.
600 cycles from 0% DOD to 80% DOD.
So the math in my original post applies.
This is from Trojan’s AGM application guide.
Lots of other variables here like how long the battereis remain discharged, etc.

This is correct, IMO, and the math is actually quite simple if you turn it into lifetime battery discharge amp hours then make a graph.


All this is in the earlier threads on the forum including the graphs.

[Davydd]

Originally Posted by booster

Did they ever tell you how much capacity your old van lost of the years?

I did trade it back in but I didn't know of this 3 years ago and didn't ask. I thought it was imperceptible after 6 years of ownership. It was the same general percent usage overnight and charged back up in the same amount of time. The usage varied but I checked the recharge times just like I check gas mileage just about for every fill up. It is an inexact check but I never sensed an 80% difference like the Ards with the same batteries. Like I mentioned, they stored their RV on black asphalt for 6 months over the summer in Phoenix.

BTW, when I traded it back in they said they had taken back every van except one. They refurbish and update them with current practices when they can with them and sell them to other customers. I don't know the extent of refurbishment of mine and don't know who bought it. Only about 30 ARV RVs attend ARV Fest every year and I know most of those owners. ARV continuously improves and gives you a feeling of "Damn if I didn't think of that when I bought mine!" I put in quite a few things first anyway including the electric articulated beds that were a successful feature in subsequent vans. I don't know if anyone will adopt my bunk bed design.

ARV is pretty open with their development. This was one of their failures. They have since developed an in-house (not Volta) 48 volt system I think powerful enough to air condition a Class B overnight. "Damn, I bought too soon!"

https://www.youtube.com/watch?v=o05uUcpv8CI

[MsNomer]

Originally Posted by avanti

...or have enough AGMs capacity to handle the load. Our Legend had 440Ah of AGM and we never had a low-voltage problem under any reasonable conditions.

Same problem—wasted capacity—just on a larger scale.

[Davydd]

I have 576ah of lithium in my currant 144 2500 Sprinter van. The equivalent with AGMs couldn't equal that because of too much weight and space taken up which there was no where to put them. I could have gotten 864ah of batteries but I didn't think I would need them and opted for two under bed drawers where I had the batteries.

[avanti]

Originally Posted by Davydd

I have 576ah of lithium in my currant 144 2500 Sprinter van.

At what voltage? I.e., how many watts?

[Davydd]

Originally Posted by avanti

At what voltage? I.e., how many watts?

Four Lithion U27-12XP 12.8 V | 144 AH | 19.2 KG | PN# 1008773 batteries

https://www.lithionbattery.com/produ...s/u-charge-xp/

[InterBlog]

Originally Posted by booster

…
… we haven't yet heard what she plans on doing to make her next lithium batteries last longer.

I don’t have a full answer yet, other than the following administrative controls:

(1) DON’T BUY ANY LITHIUM BATTERIES UNTIL THEY ARE ABSOLUTELY NEEDED. I tend to be preparation-minded and I buy things preemptively, especially since the point where inflation started running wild. In January 2023, I bought an EcoFlow DeltaPro as a supplemental battery to use primarily in our utility trailer which has 600 watts of solar on its roof (and also for non-travel-related hurricane prep), because at that point Costco was offering it for $2,800 when every other vendor was still at the $4,000 price point. I didn’t need it right away, but that seemed like it might be the pull-the-trigger price. In the future, I will be figuring the “death curve” into my purchasing decisions.

(2) DO YOUR OWN CAPACITY TESTING ON ANY NEW LITHIUM BATTERY THAT YOU DO BUY. Verify that you have not been sold aged stock under the guise of a new product. Trust nothing.

(3) FOLLOW ALL SOC MAINTENANCE INSTRUCTIONS TO THE LETTER, AND KEEP A WRITTEN LOG. We already mentioned the procedures that EcoFlow now stipulates for the DeltaPro.

(4) MY NEXT CLASS B HOUSE BATTERY WILL BE CARTRIDGE-STYLE AND WILL BE REMOVED FOR STORAGE IN AN AIR-CONDITIONED SPACE WHEN THE VAN IS NOT IN USE. We talk about cassette toilets all the time, but I don’t ever recall any DIYer developing a “cassette” system in which the lithium is detached for protective storage (my engineer husband has already begun designing a docking station for our next battery). This may not be an important step if one’s van spends much of its life in Minnesota, but look at this image below, which I took yesterday as I was leaving my gym, where the only exercise I can do these days is lap swimming because Houston’s infrastructure is not designed to keep up with this intensity of heat, which is about 15 degrees above our normal, and so the gym is hot (it’s LA Fitness, with the cavernous interior that is characteristic of the franchise - ceilings about 25 feet high). I took this photo while I was ROLLING, not parked on asphalt where heat may accumulate and distort the car’s reading. This summer’s heat wave has been a game-changer in multiple respects - the Wall Street Journal published a piece the other day where they explored the phenomenon of people becoming nocturnal because it’s just not survivable otherwise. Anyway, as I’m driving back to my house, I’m thinking about my Class B and the fact that there is no practicable way for me to remove my existing battery during all of this scorching hell. That has to change, and it is one factor that I can control in the future.

EDIT - the photo is a little blurry. In case you needed confirmation, it says 109 degrees F.

[Davydd]

Minnesota? The concern for us is cold. Storing outside you would need shore power to keep batteries heated or you would have to detach and store them in a controlled temperature space. Just once I did experience a -43F temperature which would kill a lithium battery.

How would one do a cassette system? My current van has four group 27 cases but still you have to attach two terminals to each battery. The heating is a 12V plate under the batteries powered by the batteries thus you would need shore power over longterm storage. It would be easy to detach and move but it is not a plug in cassette.

In my previous ARV van I had a setup like Technomadia but with heating pads sandwiched between the modules and a similar block of batteries to that in the video of ARV's biggest mistake. Way too complex for me to deal with it. With those batteries they were under the van in a fiberglass waterproof enclosure housed with an iron cage and a skid plate. I think they said it was 500 lbs. and they installed and pulled it up on a lift.

[@Michael]

Originally Posted by InterBlog

... but I don’t ever recall any DIYer developing a “cassette” system in which the lithium is detached for protective storage (my engineer husband has already begun designing a docking station for our next battery). This may not be an important step if one’s van spends much of its life in Minnesota, ...

Important even here - to prevent damage from the cold. Mine is heated now, but before that I removed it during severe cold spells. If I were to leave it over winter in a place with no shore power, I'd pull it out. Easy to do if using 'drop-in' batteries.

...(1) DON’T BUY ANY LITHIUM BATTERIES UNTIL THEY ARE ABSOLUTELY NEEDED. I tend to be preparation-minded and I buy things preemptively, especially since the point where inflation started running wild.

A good plan for any technology that drops in price over time.