Battery Analysis: LiFePO4/AGM/FLA

BobC · 01-04-2021, 08:22 AM

I ran across a video the other day that presents an extensive analysis and comparison of LiFePO4, AGM and Flooded Lead Acid batteries in terms of performance, cost, capacity, etc.

The presenter, Tom Morton, is an electrical engineer and the analysis presented in the Youtube video is an engineering oriented analysis. As such, it is packed with numbers, graphs, etc., is fast moving and may not be for everyone. Those with a mathematical/analytical/engineering bent will most likely love it whether they agree with him or not.

I'm sure others are familiar with his and his wife's Youtube channel and blog, "Mortons on the Move" but they're new to me.

https://www.youtube.com/watch?v=iy3hga_P5YY&t=1s

https://mortonsonthemove.com/

DavidM · 01-04-2021, 09:58 AM

I didn't spend 36 minutes watching that video, and yes I am an engineer. Here is my take on the cost per usable amp hour. That is only one of the variables though. Quick charging, low temperature usability, self discharge rate, weight, etc are some of the others. You can quibble about sale prices, and usable capacity. Perhaps the slow charging rate for FLA, AGM and Firefly's from 85%+ limits the usable range to 50-85%, but solar charging usually moderates this limitation.

Golf Cart FLAs $2.00 per usable amp hour
Generic AGMs $4.00
Name brand AGMs $6.00+
Firefly Carbon Foam* $6.25
SOK low cost LiPO $5.50
Battle Born LiPO $9.00

*Not sure if I believe their 80% DOD claims.

David

BobC · 01-04-2021, 10:41 AM

Quote:

Originally Posted by DavidM

I didn't spend 36 minutes watching that video, and yes I am an engineer. Here is my take on the cost per usable amp hour. That is only one of the variables though. Quick charging, low temperature usability, self discharge rate, weight, etc are some of the others. You can quibble about sale prices, and usable capacity. Perhaps the slow charging rate for FLA, AGM and Firefly's from 85%+ limits the usable range to 50-85%, but solar charging usually moderates this limitation.

Golf Cart FLAs $2.00 per usable amp hour
Generic AGMs $4.00
Name brand AGMs $6.00+
Firefly Carbon Foam* $6.25
SOK low cost LiPO $5.50
Battle Born LiPO $9.00

*Not sure if I believe their 80% DOD claims.

David

His analysis covers some, if not all, of the other variables you mention.

Old Navy · 01-04-2021, 06:45 PM

Great coverage of the differences and advantages. If you know how you will be using your batteries, this information can certainly help you make a more informed decision.

Not that it would have had much impact on his conclusion, but he shouldn't have been shocked that the brand new lead acid batteries didn't measure to full capacity. He should have known that lead acid batteries take up to 50 cycles to reach 100% capacity. Virtually all Deep Cycle manufacturers include this info in their spec sheets.

Battery University

From the link:

Quote:

Deep-cycle batteries are at about 85 percent when new and will increase to 100 percent, or close to full capacity, when fully formatted.

He also used a price of $1600 for 2X BB batteries, not $1900, giving them a 15% greater advantage in the $/Ah and $/Wh comparisons. I don't mean to pick apart his analysis, but these seem like 2 pretty glaring errors. Still lots of good information explained in simple terms.

tderonne · 01-05-2021, 09:00 AM

I was disappointed in his using state of charge and cutoff voltage interchangeably. He started talking about it a little more correctly at the end when he mentioned recovery voltage, but didn't say much about how the recovery voltage relates to state of charge. Using a loaded voltage as an indicator of state of charge is wrong, and his results show that.

I also didn't like how often he said "extrapolated". As an engineer he should know what that means. Sometime he was actually interpolating, others he was simply looking at the data, not extrapolating or interpolating at all.

DavidM · 01-05-2021, 10:55 AM

Quote:

Originally Posted by tderonne

Using a loaded voltage as an indicator of state of charge is wrong, and his results show that.

Yes, that is so wrong. Using loaded voltage as an indication of state of charge invalidates the whole thing. Some engineer!!!

FWIW, at best after resting for an hour, battery voltage is a very approximate indication of state of charge, probably only good to +/- 20%. When you put a load on the battery and with increasing load, the voltage drops, often making it only accurate to +/- 50%.

I have confirmed this over years of watching battery voltage, load and actual state of charge as measured by a shunt based battery monitor. And yes I am an engineer as well. How else would I know this nerdy stuff

.

David

BobC · 01-05-2021, 01:03 PM

Great comments and good, critical thinking.

1237dmctlc · 01-10-2021, 05:58 PM

I've seen a few others like thus with different brands and reviews. I agree with all that was said but I have to add to that that it covers certain brand of each type of battery and we know not all are created equal. So unless you only want to use one of those particular brands and types I feel the variables mention and cost could vary significantly the end cost. I'm no expert but I understand the technicalities of testing and their approach being an EE also.

Journey39n · 01-10-2021, 07:11 PM

I am an old engineer, and loved all the detail.

However, I have my own 'real world' use to rely on. No muss, no fuss, four CostCo GC2 batteries, wired to be 2 banks of 12v, mounted on a 1/2" rubber pad, Temp operating range, over 100 spring & summer, 20 and up in winter, but mostly 50-70 degrees. When boondocking, various lights, appliances, TVs, etc. generator charged 2 hours in the morning, 1 hour at night. Definitely 3-4 hours of TV watching at night. Usual voltage range on inverter, starts at 12.5v at night, 12.0v or so in morning for the first 8 years, last two, down to 11.9v in morning now that we have added a compressor cooling unit to our Norcold refer.

Results, first set of 4 batteries, cost $75 each, lasted 6 years. So far, three years into the second set that cost $83 each. For others, it might be nice to have the latest and greatest Lithium batteries and associated electronics. But for our use, and 'real world' experience, the old standard GC2 lead acid batteries are doing fine.

thataway4 · 01-10-2021, 08:30 PM

One valid point made in the video is the use of wattage, instead of amp hours. Since the Li battery starts at a higher voltage (13.5 +/- Volts) and slowly goes to 12.8 Volts at 20% SOC, and is at 12.0 Volts at 10% SOC, there are more watt/hours available...The FLA battery is 50% discharged at 12.2 volts (steady state) at 25% SOC at 12.0 Volts and by 11.8 volts is depleted. I have not monitored the voltage (since I watch amps on the Victron meter and SOC) when the my inverter is running a 1200 watt microwave, but my impression is that the voltage is maintained with the LiFePO4 battery. I'll watch voltage next time I use it and confirm my impression.

In my RV I use Golf Carts, in my boat where weight is more critical, I use the LiFePO4--also the boat is mostly off grid, and the RV is mostly on grid, at least for the night.

Elkman · 01-13-2021, 03:19 PM

Theory only takes you so far. With my two new Lithionics 125AH batteries I can take them from a 50% SOC to 100% SOC with an hour of run time with the Onan generator which is putting out 40 amps and which the batteries can accept. With the new lead acid batteries installed at Winnebago the same SOC recovery took more than 3 hours.

Running a generator 30 minutes each day as compared to running it for 3 or more hours each day is important to me and well worth the cost of the new lithium phosphate batteries. It also helps with the terrible output of 1.0 amp from the Winnebago installed Zamp solar kit.

BobC · 01-13-2021, 05:31 PM

Quote:

Originally Posted by Elkman

Theory only takes you so far. With my two new Lithionics 125AH batteries I can take them from a 50% SOC to 100% SOC with an hour of run time with the Onan generator which is putting out 40 amps and which the batteries can accept. With the new lead acid batteries installed at Winnebago the same SOC recovery took more than 3 hours.

Running a generator 30 minutes each day as compared to running it for 3 or more hours each day is important to me and well worth the cost of the new lithium phosphate batteries. It also helps with the terrible output of 1.0 amp from the Winnebago installed Zamp solar kit.

Wow, that's interesting, especially since I hate generators running for hours. What model controller and how many watts of panels do you have? One amp just doesn't seem right unless your batteries are almost charged. My understanding is that a solar controller will only output what your batteries "need", based on its battery type setting.