Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×


Reply
 
Thread Tools Display Modes
Old 05-23-2024, 08:39 AM   #1
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Your LiFePO4 batteries aren't as good as you think they are

The self-discharge rate of my LiFePO4 batteries is around 2~3% per month. I expect that this is typical for all LiFePO4 batteries, all brands. The cells these vendors use to assemble their battery packages come from common factories. The self-discharge current won't be measured by an external shunt monitor. And I suspect it won't be measured by the battery BMS either. The self-discharge current is happening inside the individual cells of the battery package.

I've seen lots of comments on this forum which makes me think many people believe their Li batteries are holding a 100% charge for very long durations. They are not. If you have a shunt monitor programmed for your battery bank's full capacity, once it reaches a 100% display it will keep the value at 100% and continually reset its full reference point as more charge current flows into the battery. That's how my shunt behaves and I presume other brands of shunts are the same.
If you want to learn what your battery's actual self-discharge is doing, reprogram your shunt for double your battery capacity so that it reads 50% when full. Then after a month or so in storage reconnect your battery to the converter and watch another 2~3% of charge flow in. Do this over several months in off-season storage and it will add up to give you a good monthly average.

For example, my battery bank is 300Ah. My shunt is set higher than that. Setting it to double (600Ah) makes the percentages math simpler, but the real point is to see the extra amp-hours so any higher value will do. After one month my shunt will indicate 306Ah SoC when the battery is full. After 2 months, 312Ah, etc. It doesn't matter if you leave the battery disconnected or if you leave things connected and on shore power while idle. The same amount of extra current will trickle into the battery from the converter over a month's time if it's stored "live". And actually you don't need to do this while in storage. Just set your shunt to a higher value and leave it that way all the time, and watch the "full" value creep up during the active camping season, month after month. The self-discharge inside the cells is always happening and will be replaced with each charge cycle.

I'd be interested in seeing the measured results of different battery brands that people have. The batteries I've characterized here are LiTime.
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 08:51 AM   #2
Trailer Park Supervisor
 
NJKris's Avatar
 
Join Date: Sep 2018
Location: Northern NJ
Posts: 8,894
I've got a Weize 100ah down basement past 2 years, it's still around 50%. Been awhile since I checked it, I should.
__________________
2019 Rockwood Geo Pro G19FD w/off road package
2015 Ford F150 XLT Super Cab 4x4 V8
Yes, I drink the water!
NJKris is offline   Reply With Quote
Old 05-23-2024, 08:52 AM   #3
Senior Member
 
Join Date: Apr 2022
Location: Tarpon Springs FL
Posts: 3,959
Changing a shunt setting has no effect on battery
It just gives you a different calculation and battery reading
————————————-
There is a small battery self discharge most manufactures will tell you what is best for storage
Charge up battery every 6 months 12 months 18 months
It is not that bad having to do a charge once in a while

Cells are made by only a few companies their performance is fairly stable and failures are more to do with wiring and BMS problems

Good thing is. Wiring and BMS can be replaced/repaired instead of just buying new battery
__________________
Tarpon Springs FL
2022 Salem 24RLXL
Aussieguy is offline   Reply With Quote
Old 05-23-2024, 08:56 AM   #4
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Quote:
Originally Posted by NJKris View Post
I've got a Weize 100ah down basement past 2 years, it's still around 50%. Been awhile since I checked it, I should.
That works out to 2.1% per month self-discharge.
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 08:58 AM   #5
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Quote:
Originally Posted by Aussieguy View Post
Changing a shunt setting has no effect on battery
It just gives you a different calculation and battery reading
I hope you didn't think my post implied anything different.
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 09:00 AM   #6
Trailer Park Supervisor
 
NJKris's Avatar
 
Join Date: Sep 2018
Location: Northern NJ
Posts: 8,894
Quote:
Originally Posted by jlankford View Post
That works out to 2.1% per month self-discharge.
It was about 50% when I put it down there 2 years ago though.


edit: Just checked it, sitting at 13.13 vdc. I guess that's closer to 60%. Hasn't budged in almost 2 years. I really need to install this thing.
__________________
2019 Rockwood Geo Pro G19FD w/off road package
2015 Ford F150 XLT Super Cab 4x4 V8
Yes, I drink the water!
NJKris is offline   Reply With Quote
Old 05-23-2024, 09:30 AM   #7
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Quote:
Originally Posted by NJKris View Post
It was about 50% when I put it down there 2 years ago though.


edit: Just checked it, sitting at 13.13 vdc. I guess that's closer to 60%. Hasn't budged in almost 2 years. I really need to install this thing.

OK, well that's curious. Of course we all know it's hard to accurately gauge what the Li battery SoC is from just voltage readings.
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 09:51 AM   #8
Senior Member
 
Join Date: Apr 2022
Location: Tarpon Springs FL
Posts: 3,959
Quote:
Originally Posted by jlankford View Post
I hope you didn't think my post implied anything different.
Kinda did .. now makes more sense


You Set shunt to higher value for battery
Only look at amp in /out gives you capacity in ah

It is NOT calculating a percentage which would require exact battery peramiters
Aussieguy is offline   Reply With Quote
Old 05-23-2024, 10:09 AM   #9
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Quote:
Originally Posted by Aussieguy View Post
Kinda did ….. now makes more sense


You Set shunt to higher value for battery
Only look at amp in /out gives you capacity in ah

It is NOT calculating a percentage which would require exact battery peramiters

Right. I'm just describing a method to use the shunt as a tool to measure the normally "unseen" self-discharge amount.

FWIW, I "do" use the shunt's percentage display, though. If I set the full reference to exactly 50% at the shunt, then when I see it reading e.g. "53%", then I know that 6% extra capacity has flowed into the battery since the reference was last set (53% == 106% == an extra 6% charging has occurred. It's why I double the high setting to simplify the percentage quick calculation)
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 10:11 AM   #10
Senior Member
 
Join Date: Jan 2013
Location: Space Coast of Florida
Posts: 4,072
I dont own Lithium batteries but Im trying to figure out the reason for the worry about a few percent discharge a month when a battery is not used?

Before you go camping, charge it. If it is sitting for long periods, charge it.
__________________


2016 Siverback 33IK, Towed 50K+ mile
2018 Ford F-350 Lariat 6.7L V8 Diesel 4WD Crew Cab

"If you don't know where you are going, any road will get you there."
dalford is offline   Reply With Quote
Old 05-23-2024, 10:19 AM   #11
Senior Member
 
Join Date: Jul 2023
Location: Waynesville, NC
Posts: 315
Quote:
Originally Posted by dalford View Post
I don’t own Lithium batteries but I’m trying to figure out the reason for the worry about a few percent discharge a month when a battery is not used?

Before you go camping, charge it. If it is sitting for long periods, charge it.

There's no worry. I'm not bashing Li batteries at all - I'll never go back. With this post I'm simply trying to correct misconceptions some people have that the batteries miraculously hold a charge indefinitely. I guess it's the OCD in me that wants to correct this misinformation and to characterize the amount of self-discharge for my own information.
__________________
2023 r-pod RP-192 with Beast Mode suspension
600W rooftop solar, 300Ah LiFePO4 battery bank, 2000W inverter.
Uses an electric coffee maker when boondocking.

"Never underestimate the power of human stupidity."
-Lazarus Long
jlankford is online now   Reply With Quote
Old 05-23-2024, 10:31 AM   #12
Senior Member
 
Join Date: Jan 2013
Location: Space Coast of Florida
Posts: 4,072
Quote:
Originally Posted by jlankford View Post
There's no worry. I'm not bashing Li batteries at all - I'll never go back. With this post I'm simply trying to correct misconceptions some people have that the batteries miraculously hold a charge indefinitely. I guess it's the OCD in me that wants to correct this misinformation and to characterize the amount of self-discharge for my own information.
LOL..I know what you mean by OCD I guess if I ever go with Li batteries I would never go back either. Im not set up to boondock and have only done it a few times. Generator needed for sure.
__________________


2016 Siverback 33IK, Towed 50K+ mile
2018 Ford F-350 Lariat 6.7L V8 Diesel 4WD Crew Cab

"If you don't know where you are going, any road will get you there."
dalford is offline   Reply With Quote
Old 05-23-2024, 09:17 PM   #13
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 17,456
Quote:
Originally Posted by jlankford View Post
There's no worry. I'm not bashing Li batteries at all - I'll never go back. With this post I'm simply trying to correct misconceptions some people have that the batteries miraculously hold a charge indefinitely. I guess it's the OCD in me that wants to correct this misinformation and to characterize the amount of self-discharge for my own information.
It's the internet and you'll never correct the misinformation that's freely passed around.

Lifepo4 batteries do have a lower rate of self discharge but that's not why most like them.

Less weight, more usable energy, ability to charge faster, ability to install inside the RV, and huge cycle life, all overshadow the smaller self discharge rate.
TitanMike is offline   Reply With Quote
Old 05-25-2024, 10:47 AM   #14
Senior Member
 
Join Date: Apr 2020
Posts: 735
Keep in mind, the shunt itself draws power. Particularly the early bmv 712’s, until victron changed them. About 20ma iirc. This may account for some of your maths.
__________________
2019 F150 HDPP 4X4 3.5. 2500lb payload.
2018 Rockwood 2506
Half Ton Heavy is offline   Reply With Quote
Old 05-25-2024, 11:41 AM   #15
Senior Member
 
Join Date: Jul 2017
Location: North of Seattle, WA
Posts: 17,456
Quote:
Originally Posted by Half Ton Heavy View Post
Keep in mind, the shunt itself draws power. Particularly the early bmv 712’s, until victron changed them. About 20ma iirc. This may account for some of your maths.

True. However this small current draw is not captured by many monitors as even the best have a 0.1v threshold. Below that the data may or may not be captured.

You really don't know the cumulative amount drawn by BMS and Monitor/Shunt until you perform a complete charge after period of storage that began ot 100% SOC with all loads disconnected ( including "detectors", etc)
TitanMike is offline   Reply With Quote
Old 05-25-2024, 11:53 AM   #16
Senior Member
 
Join Date: Aug 2023
Location: Bayou Vista, TX
Posts: 244
Quote:
Originally Posted by TitanMike View Post
It's the internet and you'll never correct the misinformation that's freely passed around.

Lifepo4 batteries do have a lower rate of self discharge but that's not why most like them.

Less weight, more usable energy, ability to charge faster, ability to install inside the RV, and huge cycle life, all overshadow the smaller self discharge rate.
And don't forget, LiFePO4 batteries are NOT the same type of batteries you see catching fire in phones and laptops. Those are LiPo. LiFePO4 (Lithium Iron Phosphate) are very safe as long as you don't try charging them below freezing. Until something even better comes along in the future, I'm sticking with mine, and will be adding more.
__________________
2021 Forest River Wildwood 171RBXL
Towed by 2018 Toyota Tundra TRD SR5
reidfo is offline   Reply With Quote
Old 05-25-2024, 04:56 PM   #17
Senior Member
 
Hclarkx's Avatar
 
Join Date: Jan 2015
Location: Granite Bay, Ca
Posts: 1,095
Quote:
Originally Posted by TitanMike View Post
True. However this small current draw is not captured by many monitors as even the best have a 0.1v threshold. Below that the data may or may not be captured.

You really don't know the cumulative amount drawn by BMS and Monitor/Shunt until you perform a complete charge after period of storage that began ot 100% SOC with all loads disconnected ( including "detectors", etc)
This ^^^^^^^^^^

I think you meant 0.1 Amps but close enough.

The BMV-712 can sense currents (charge and discharge as low as 0.1 amps though I don't know that this is the default (other settings are all higher).

Some BMSs do not sense and account for currents under 1 amp. LiTime is 1 amp. Lifeblue is 0.7 amp (or was a few years ago).

The problem is that the A/D (analog to digital) conversion is tricky and most monitor makers and BMS makers don't invest a lot in a precision A/D or smoothing to eliminate the noise.

In fact, I think the BMV-721 is the only monitor that gets down to 0.1 amp (and the instructions say to raise the setting if it fluctuates in appropriately.

The 20 ma BMS load is, of course well below any BMS current sensing threshold (and an external monitor doesn't see it) Some BMSs draw more than 20 ma. The ones drawing 20 ma will take the LFP down 14.4 Amp hours over a month. I think most BMSs have a sleep function so they aren't as problematic as this calculation suggests.

So assessing battery self-discharge is really not possible with these devices unless you know the current sensor threshold AND keep the current above that threshold (which, of course makes the self discharge calculation far more difficult and downright impractical). In addition, the load current and charge current sensing thresholds might not be the same.

So, with no good way to tightly monitor charging and discharging current and no information on the BMS design, using such systems to estimate self discharge is fruitless.

As for getting the SOC to, say, 50%, and letting it sit for a month or two and charging it back to 50% not only has all of the monitor problems I and others have mentioned, but there's an addition problem. Lots goes on inside of the LFP when you apply a charger to a resting battery, including temperature changes which require energy. And BMS losses, albeit small ones. But, here there are chemical things involved as well that have to happen before charging is effective. Try topping off an LFP and disconnecting the charger (and load) and watching the voltage. It will settle back to 13.34 Volts over some hours with only the load of the BMS and self discharge drawing it down. Then top it off again. You will find it needs several amp-hours to get back to 100% SOC even though only a fraction of that was withdrawn since the last top-off. Some of this may be in the monitoring, but there are other mechanisms at play even if the monitoring were perfect; i.e., chemical things.

Voltage can be used to estimate LFP SOC fairly accurately. There is about a 0.3 to 0.4 voltage difference between 20% SOC and 90% SOC (it's not a straight line). But, here again, without a resting voltage curve over this SOC range for your battery, it's not going to work. One could look at some resting voltage curves found on the internet and do a straight line approximation over a short range and get fairly close. It might take a six month discharge to see results. And, as above, you do need to know your BMS behavior which none of us do. Now, if you are lumping your BMS power draw in with self-discharge, one could do this. But, it would be a tedious process.

Or not worry about it and just charge the LFP before hitting the road.
__________________
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L
2015 30' 8280WS Rockwood Ultra Lite
Solar, LiFePO4, 12V fridge, mini split
100% dry camping and boondocking.
https://hclarkx.slickpic.com/gallery/?viewer
Hclarkx is offline   Reply With Quote
Old 05-26-2024, 06:09 AM   #18
Senior Member
 
rk06382's Avatar
 
Join Date: Oct 2016
Location: Alaska
Posts: 1,854
SOC on a BMV-712 is calculated, not measured.

It is like the your dashboard saying "399 Miles to Empty."

I have used my BMV-712 since 2018. One time I was confused when after working on the battery cables. I had 65% SOC before I replaced the cables. But after I powered it back up, I had 100% SOC. (BMV-712 has a default setting to start at 100% SOC when powered up.)
__________________
Robert
2018 FR3 28DS | Boondock 99% of the time
Samlex EVO-3012 Inverter/Charger | 600ah Battle Born LiFePO4 | Victron BMV-712 & MPPT 100/50 | 800W Renogy Solar | Fan-Tastic Fans | Blue Ox TruCenter | SnapPads | SumoSprings | Koni Shocks | RVLock
Solar Power & Battle Born batteries
rk06382 is offline   Reply With Quote
Old 05-26-2024, 06:43 AM   #19
Senior Member
 
Join Date: Aug 2018
Posts: 503
I guess this is a concern for the theoreticians, for most people's LiFePo4, are getting touched by either solar, TV, or shore power periodically. Make your battery bank sufficiently large and don't worry about such stuff.
__________________
NOBO 2023 20.3 Beast suspension, std. solar pkg
too many mods and repairs to list
4x100ah LifePo4
2019 Ford Expedition Max, payload ~ 1700

Former - 2019 NOBO 19.7
DES-1 is offline   Reply With Quote
Old 05-26-2024, 03:13 PM   #20
Senior Member
 
Hclarkx's Avatar
 
Join Date: Jan 2015
Location: Granite Bay, Ca
Posts: 1,095
Quote:
Originally Posted by rk06382 View Post
SOC on a BMV-712 is calculated, not measured.

It is like the your dashboard saying "399 Miles to Empty."
Well, not really. It is calculated, but it is a coulomb counter and does so by calculating coulomb flow from from current measurements. Voltage measurements are pretty good these days. The sensing and A/D conversion is pretty good. Current? Not so much. The problem is noise that can skew the measurement.

Under light load conditions the BMV-712's current reading may be sending out 0 amps when actual current exists but is below 0.1 amp.

The BMV-712 can't calculate (accumulate) if it does not have enough current to trigger the current sensing. So, let's say the BMV does not see a 0.09 amp load. That's potentially 15 amphours per week if load current is always under 0.1 amp. So the BMV has a potential error accumulation of 15 amphours per week (usually much less than that, of course).

Some BMS need one amp of current to turn on current measurement. HiTime is one example. Lifeblue is 0.7 amps (the last time I had one).

It's unfortunate, but the BMV-712 and all BMSs need to be recalibrated often. This occurs when the battery is topped off. Some of us solar users that dry camp exclusively, may not top-off for weeks and thus live with significant error in our SOC readings.

This said, the BMV-712 is surely the best game in town given it's 0.1 amp threshold (my Overkill BMSs are 0.3 amp).

Try this. When you next charge your LiFePo4 battery, watch the SOC percentage as the voltage hit's top-off voltage (a bit above 14 Volts). The SOC will suddenly switch to 100%. The SOC just before that will be lower, maybe several percent lower (I've seen 17% lower from my BMSs when I had marginal solar and was on the cloudy California coast for weeks).

There are several reasons why the SOC reading usually drifts down between top-offs. Often there are only small loads (below current sensing threshold) at night. Some charging (early morning and late evening with solar) is below the current threshold so is neglected.
__________________
2020 GMC Denali 2500HD Crew 4X4 Gas 6.6L
2015 30' 8280WS Rockwood Ultra Lite
Solar, LiFePO4, 12V fridge, mini split
100% dry camping and boondocking.
https://hclarkx.slickpic.com/gallery/?viewer
Hclarkx is offline   Reply With Quote
Reply

Tags
batteries

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by Forest River, Inc. or any of its affiliates. This is an independent, unofficial site.



All times are GMT -5. The time now is 07:36 PM.