Lithium batteries discharging

edlynnrich

Escape Reality Lancaster, Va 2022 21C
RV LIFE Pro
Joined
Jan 6, 2014
Messages
157
Location
Lancaster, Va
After being away for 9 weeks I checked on the trailer and discovered that the batteries were down to 11.2 volts as measured by a Victron battery monitor. We have 2 ETI installed Go Power 100 ah batteries in our 2022 21C. The batteries were disconnected at the battery disconnect switch and the solar panels were disconnected by a switch that I installed (thank you forum members for your advice on that project). I discharged the batteries to 50% as recommended for storage. I did not have any discharge issues last winter but I may have taken an extra step and disconnected the battery cables but I don’t recall. What would have that much of a draw to pull the batteries down like that? I’ve attached some screenshots of the Victron connect display for the last 60 days. When the batteries are fully charged I’ll bring them down to 50% and disconnect the cables as I probably should have earlier. I appreciate any input that you electrical wizards may have. Thanks
 

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Do the batteries have internal heaters? Maybe the disconnect switch isn't disconnecting? Is anyone familiar with how ETI wires the emergency brakes? Do they still function if the disconnect switch us thrown? If so, maybe a malfunctioning emergency brake module?
 
Do the batteries have internal heaters? Maybe the disconnect switch isn't disconnecting? Is anyone familiar with how ETI wires the emergency brakes? Do they still function if the disconnect switch us thrown? If so, maybe a malfunctioning emergency brake module?
It's my understanding that the internal battery heaters do not use the battery itself for heating but rather supplied power from the solar panels or the converter. That would really suck if they used the battery itself because every time they got cold they would drain themselves trying to keep warm. Yes the e-brakes still work if the disconnect is thrown.
 
I don’t believe my batteries have heaters but I wouldn’t put any money on it. I’ll have to check. As for the emergency brakes I don’t see how they would fail to a closed circuit mode but I’ll check it out just to be sure.
 
You'll have to hunt for phantom drains - like the emergency brakes, for example. Best to use a multi-meter on the amp setting. Stay within the limits of the meter or you will blow the internal fuse. A simple but effective alternative is use an automotive 12V light bulb and hold it between the negative battery terminal and the ground wire. It should not light with everything turned off. If it lights - just a glimmer perhaps - then something is asking for battery power. And remember, in this test the (-) battery terminal is ground, the ground wire is (+).

But a reminder: All trailer LiFePO4 batteries have a BMS. That internal computer circuit will be pulling a couple of milli-Amps 100% of the time. It can not be disconnected. That is why the manufacturers recommend the occasional charge while in storage.

One option. To winterize your (lithium) batteries bring them down to 80%, rather than 50%, prior to long storage.
 
It's my understanding that the internal battery heaters do not use the battery itself for heating but rather supplied power from the solar panels or the converter. That would really suck if they used the battery itself because every time they got cold they would drain themselves trying to keep warm. Yes the e-brakes still work if the disconnect is thrown.

thats correct. if they are too cold to be charged, they divert the applied charging power to the heater until they are warm enough. Mine don't have heaters (they were a new thing in late 2021 when i bought them) but if I did it again, I'd undoubtedly get the heaters, even tho in fact I've never needed them yet. I'd probably also get batteries with internal bluetooth monitoring, as an external shunt like my Victron SmartShunt doesn't know that some of the charging power went into the heaters so will be wrong until the batteries hit 100% again and the monitor can reset.
 
Would the internal BMS explain the rapid voltage drop (the voltage curve looks like it fell off a cliff) without the Victron shunt registering any power or current draw? I truly appreciate everyone’s input as I’m learning something new from the forum all the time.
 
I think that voltage curve looks like a normal LFP discharge as it is approaching fully depleted. Self discharge of LFP is around 3% per month. BMS power consumption depends on the BMS but it is almost certainly very small. Even if the BMS and shunt were using 10mA, it would still only represent an additional 3.5% per month.

What I’m wondering is how you determined the original 50% starting point. Did you charge up to 14.6v and then discharge as you said you are doing now, or did you just discharge from wherever it was at until the shunt said 50%? It is possible for a shunt readout to become progressively less accurate if the battery hasn’t been fully charged or fully discharged in a long time. Perhaps the readout said 50% but the true state of charge was quite a bit less.
 
Try this again.

Hey Michael, I think you are on to something there. It was over a year ago but I’m pretty sure I just ran it down to 50% on the Victron display. I just learned something else.
 
Thanks for posting this video Perry. Will Prowse debunked a myth I was following about charging to 100%. I had my charge regimen set up to charge to 80% and only charge to 100% every 10 cycles or so. I’ll need to change my charging profile. I appreciate Will’s videos in that his teaching is clear and understandable for a neophyte like me.
 
After being away for 9 weeks I checked on the trailer and discovered that the batteries were down to 11.2 volts as measured by a Victron battery monitor. We have 2 ETI installed Go Power 100 ah batteries in our 2022 21C. The batteries were disconnected at the battery disconnect switch and the solar panels were disconnected by a switch that I installed (thank you forum members for your advice on that project). I discharged the batteries to 50% as recommended for storage. I did not have any discharge issues last winter but I may have taken an extra step and disconnected the battery cables but I don’t recall. What would have that much of a draw to pull the batteries down like that? I’ve attached some screenshots of the Victron connect display for the last 60 days. When the batteries are fully charged I’ll bring them down to 50% and disconnect the cables as I probably should have earlier. I appreciate any input that you electrical wizards may have. Thanks
I've got a 2023 E19 with 3 Lithium batteries and I've found that there is lots of misinformation, and a lack of information on the things I'd like to know. I don't know if the 50% discharge for storage is wrong, but where did that come from, and what is the basis for it? I will store mine at full charge until this makes sense. And as far as I have been able to determine, the BMS does not have a battery heating function. The BMS shuts off the output and won't allow charging at low temperature (about 35 deg.F), but it doesn't heat the battery (unless it's one of the very expensive models, like $1000 for 100 Ah). When I tried camping at about 5 Deg. F recently, there was no voltage, even though I left home with them near fully charged. I plugged in and they still would not charge. After heating the camper inside and directing a hair dryer at the batteries for close to 2 hours (I was able to get power from the host site), I heard a fairly loud click from the battery compartment, and they were back in the power business. Since then I've found that External Battery Heater Pads and Thermostats are needed to keep the batteries above about 35 degrees F to avoid having the BMS shut off the output and preventing charging. The heating pads can be powered from the batteries themselves, but it's obviously self-limiting. I plan to install the pads and supply power from a Jackery, which is a 100 Ah lithium battery that I carry for things like this. If you camp in cold weather, this appears to be an essential upgrade. Once the batteries are above 35 deg. F, and the battery compartment is well insulated and/or heat is supplied from the camper living space, they should stay above the shut-off temp. without the battery heater needing to be powered. I'll post pictures and parts info after I do my modification.
 
I have a 2023 5.0TA and I have 4 Hublion Lithium batteries from ETI that have integrated heating. My understanding is that it was the only lithium battery they offered at the time. If yours does not have it I can't explain why. I agree that external heating pads that run through the shunt would be more effective at keeping track of SOC than internal heaters as they do not run through the shunt.
 

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I've got a 2023 E19 with 3 Lithium batteries and I've found that there is lots of misinformation, and a lack of information on the things I'd like to know. I don't know if the 50% discharge for storage is wrong, but where did that come from, and what is the basis for it? I will store mine at full charge until this makes sense. And as far as I have been able to determine, the BMS does not have a battery heating function. The BMS shuts off the output and won't allow charging at low temperature (about 35 deg.F), but it doesn't heat the battery (unless it's one of the very expensive models, like $1000 for 100 Ah). When I tried camping at about 5 Deg. F recently, there was no voltage, even though I left home with them near fully charged. I plugged in and they still would not charge. After heating the camper inside and directing a hair dryer at the batteries for close to 2 hours (I was able to get power from the host site), I heard a fairly loud click from the battery compartment, and they were back in the power business. Since then I've found that External Battery Heater Pads and Thermostats are needed to keep the batteries above about 35 degrees F to avoid having the BMS shut off the output and preventing charging. The heating pads can be powered from the batteries themselves, but it's obviously self-limiting. I plan to install the pads and supply power from a Jackery, which is a 100 Ah lithium battery that I carry for things like this. If you camp in cold weather, this appears to be an essential upgrade. Once the batteries are above 35 deg. F, and the battery compartment is well insulated and/or heat is supplied from the camper living space, they should stay above the shut-off temp. without the battery heater needing to be powered. I'll post pictures and parts info after I do my modification.
Have you looked up the specific data sheets for the batteries you do have? For example here's a link to the ones from ETI I have. It's lists different temperature numbers than what you have listed above, but then I'm not sure which batteries you have.
 
FWIW, the actual research papers (not youtube videos ;) show that LifeP04 batteries are damaged more by being stored in a partially discharged state, than being charged at 100%.

I think the store partially discharged thing came from the lithium batteries in your laptop, phone,etc. Note that these are a completely different type of Lithium battery than the ones in your trailer.
 
FWIW, the actual research papers (not youtube videos ;) show that LifeP04 batteries are damaged more by being stored in a partially discharged state, than being charged at 100%.
Those research papers sound interesting. Would you mind posting a link?
 

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