Lithium batteries and depth of discharge

rh5555 · October 2023

My AGM batteries seem to be on their way out, and replacing with lithium seems to be a no-brainer. Having already established that AGM batteries can probably be discharged by 80% without loss of overall life (see previous post https://tab-rv.vanillacommunity.com/discussion/9940/agm-battery-depth-of-discharge-myth-busted/p1) and having got the impression that lithium batteries were so much better, I was a little surprised to see this in the specifications for LiTime 460Ah LiFePO4 batteries:

Cycle Life： 4000 cycles at 100% DOD, 6000 cycles at 80% DOD, 15,000 cycles at 60% DOD

While readily admitting that even 4000 discharge cycles of a Lithium battery beats out AGM batteries (and mine never made it that far), I am shocked to see that discharging to 60% will more than double the total Ah delivered by this cell in its lifetime. Is this the dirty secret of LiFePO4 batteries? They may have more cycles than you will ever need, but are they much more compromised by deep depth of discharge than AGMs?

Grumpy_G · October 2023

Technically that is true, a lead acid battery does about 2x cycles at 50% discharge vs 100% discharge. But as you already noted, the absolute number of cycles is much higher with a LFP battery. Plus, the BMS protects it from being killed by over-discharge to nothing by parasitic current draws or a forgotten light.

Marceline · October 2023

I’m not worried that I'm going to kill my battery by running it down to zero every day for more than 10 years. I’ve had it since 2019 and I’ve run it down to zero exactly once.

The key words in your post are: "They may have more cycles than you will ever need"

RTWCTS · October 2023

Here is my perspective @rh5555. If DOD is truely the concern, why not just go with a larger battery bank? 300AH will discharge to a lesser percentage than 200AH. We are a little more than a month away from the Black Friday sales. You've invested in a quality trailer with a T@B, make it 'more better' with the power you need/want. Don't let 'analysis paralysis' keep you from having the capacity you're after while on the road.

webers3 · October 2023

Here is my perspective: the LiFePO4 batteries are much better than AGM/Lead Acid and realistically they will probably outlive the ownership of your T@B. I bought a cheap $350 AmpereTime battery and haven't looked back, my advice is don't overthink it.

elbolillo · October 2023

I certainly don't claim to be an expert on battery technology. However, I think you are over-analyzing this. Take a look at this video: https://www.youtube.com/watch?v=kdsJ-rA8hTs

At the end of the day, with LiFePo4 batteries, you are gonna install them and enjoy getting into the great outdoors.

SLJ · October 2023

I installed two EnjoyBot 100AH LiFePO4 batteries last Winter. (currently about $300 each) I ran everything in my T@B including the fridge (but not the AC) during five days of solid rain with no sun and no recharging. Still had 40% left on my batteries. Typical day uses 12%-15%. I don't worry about power anymore. Best upgrade I've done.

rh5555 · October 2023

@SLJ - we. too, have camped for a week with no solar input (rain, too) running our 2-way fridge on our 225Ah AGM batteries with power to spare. That is what we used to get, and what I was expecting on our last trip. Instead the battery voltage dropped too low to run the Alde when the Victron BMV told me we had 70% state of charge remaining. Something is wrong and I haven't figured it out yet. When recharging the AGMs in bulk mode, the charge current actually went up over the first hour from 35 to 50 Amps.

I fear that we have dud batteries, which is why I started looking at lithium, only to be shocked to discover that they are way worse than AGM batteries in terms of charge cycles vs. depth of discharge. I always thought depth of discharge didn't matter (as reported in @elbolillo video), but apparently that's another myth. I completely agree that it's a moot point - even at 100% discharge I'll die of old age before I wear these batteries out. I just don't like salespeople bending the truth.

I am, however, interested to know if anyone has suffered from prematurely failing lithium batteries. I see several posts of bad AGMs and I'm wondering if Lithium (from any manufacturer) is inherently more reliable.

SLJ · October 2023

You're going to have to look pretty hard to find anyone with bad LiFePO4 batteries. I'm sure there are some but from what I've read the percentage is pretty low. Most have a built in BMS that protects them from just about anything. When I picked mine I picked them from watching teardowns for their apparent ruggedness as mine get bounced around when I'm dragging my T@B off road.

otr_320 · October 2023

We've built a number of 12v 200-300ah lifepo4 4s prismatic battery packs over the last few years. The first 200ah lifepo4 battery pack we built we brutally tested it over the course of 6 months. Cycled it over 100 times from 100% to near 0% SOC (2.700v LVD). Did a high number of .50 - .75c discharge (100-150a) and .40 - .50c charge cycles (80-100a)---very near the maximum current rating for these lifepo4 cells. Some of these tests were done in extremely cold weather (0f using heating pads). A number of hot weather tests involved powering our 10k BTU truck camper a/c unit in AZ (105-110f). At the conclusion of all these tests there was zero loss in ah performance.

The above 200ah lifepo4 battery pack weighs 38 lbs. and fits inside a small Group 24 battery box. To get anywhere near the equivalent performance (and cycle life) from lead-cell or AGM batteries would require at least 200 lbs. of lead . . . 4 times the space . . . and the purchase of 5 replacement sets of lead-cell/AGM batteries.

The difference in performance between lifepo4 and lead-cell chemistry is huge, almost laughable.

ChrisFix · October 2023

rh5555 said:

@SLJ - we. too, have camped for a week with no solar input (rain, too) running our 2-way fridge on our 225Ah AGM batteries with power to spare. That is what we used to get, and what I was expecting on our last trip. Instead the battery voltage dropped too low to run the Alde when the Victron BMV told me we had 70% state of charge remaining. Something is wrong and I haven't figured it out yet.
I fear that we have dud batteries

I have the same issue with my 2021 Harris AGMs...massive voltage drop after 50ish amps consumed. And same issue with waking up cold because the Alde gets cranky with low voltage.
There are at least two others reporting similar Harris battery failures from that same generation on this forum.
Seems we got some duds...
I'll be installing a Li Time 460ah this week, and hopefully never have to think about it again!

ckjs · October 2023

rh5555 said:

@SLJ - we. too, have camped for a week with no solar input (rain, too) running our 2-way fridge on our 225Ah AGM batteries with power to spare. That is what we used to get, and what I was expecting on our last trip. Instead the battery voltage dropped too low to run the Alde when the Victron BMV told me we had 70% state of charge remaining. Something is wrong and I haven't figured it out yet…..

We had a similar low voltage shutdown last month with our 2 Renogy 100 Ah LiFePO4 batteries. The Victron said the charge state was about 60%. However when drawing 80A for the inverter the voltage dropped to less than 12 and the batteries shut down. I suspect that one of the cables or batteries is flakey. I’m cross checking the measured voltage to the expected voltage for the charge percentage but I haven’t figured it out yet.

rh5555 · October 2023

@ChrisFix - am I right when I think the Li Time 460Ah battery that you're installing does not have a cutoff to prevent charging at low temperatures? Otherwise that battery looks amazing and I could just about cram it into our existing battery space.

ChrisFix · October 2023

rh5555 said:

@ChrisFix - am I right when I think the Li Time 460Ah battery that you're installing does not have a cutoff to prevent charging at low temperatures? Otherwise that battery looks amazing and I could just about cram it into our existing battery space.

The Li Time 460ah does not have low temp cutoff, but both the Victron MPPT controllers and the Multiplus charger I'm installing do, so that's my solution. I'm rebuilding the battery box area to accomodate both, but the battery is just 3.5" wider than the existing battery box, so really not much bigger at all.

elbolillo · October 2023

rh5555 said:

@SLJ - we. too, have camped for a week with no solar input (rain, too) running our 2-way fridge on our 225Ah AGM batteries with power to spare. That is what we used to get, and what I was expecting on our last trip. Instead the battery voltage dropped too low to run the Alde when the Victron BMV told me we had 70% state of charge remaining. Something is wrong and I haven't figured it out yet. When recharging the AGMs in bulk mode, the charge current actually went up over the first hour from 35 to 50 Amps.
I fear that we have dud batteries, which is why I started looking at lithium, only to be shocked to discover that they are way worse than AGM batteries in terms of charge cycles vs. depth of discharge. I always thought depth of discharge didn't matter (as reported in @elbolillo video), but apparently that's another myth. I completely agree that it's a moot point - even at 100% discharge I'll die of old age before I wear these batteries out. I just don't like salespeople bending the truth.
I am, however, interested to know if anyone has suffered from prematurely failing lithium batteries. I see several posts of bad AGMs and I'm wondering if Lithium (from any manufacturer) is inherently more reliable.

Battleborn says this: "Most lead acid batteries experience significantly reduced cycle life if they are discharged more than 50%, which can result in less than 300 total cycles. Conversely LIFEPO4 (lithium iron phosphate) batteries can be continually discharged to 100% DOD and there is no long term effect. You can expect to get 3000 cycles or more at this depth of discharge. "

Mickerly · October 2023

Be careful reading one company's advertising describing another company's product.

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