First Winter Storage on Lithium Iron Phosphate Batteries

Began Haven’s first winter storage in the water last month. Went to check the state of charge and the battery monitor read 56% with the battery terminals reading 12.4 volts, each of the 3 batteries. I leave the battery switch on with all DC breaker switches off except the 3 bilge pumps. The bilges are dry. I turned on the inverter/charger which quickly (1/2 hour) brought the monitors back to 100% with each battery reading 13.32 volts. My question; is 56% SOC normal after 3 weeks with virtually no draw?

“Virtually” no draw? TVs, instruments, bilge pump floats, thermostats etc can have incipient loads. Without an inverter bypass even with charger off it can suck amps.

Do you have a battery monitoring system? That should give an indication of amps out. Also think about an app that will let you view your BMK on your cell on a regular basis.

The data you reported doesn't seem to add up. How big a battery bank? Let's assume three, 100 Ah batteries or 300 Ah total. Going from 55% to 100% in 30 minutes requires a really big charger, in excess of 200 A, and actually too big for those batteries so something is wrong, probably with the SOC numbers you reported.

Lithium batteries in my limited experience (an e-bike) are just like lead acid batteries. Any DC draw will artificially reduce the voltage and therefore the implied SOC. The only way to know the real SOC is with a shunt based battery moniture. Renogy makes a good one for less than $100.

And yes over a three week period even a small parasitic draw can reduce your batteries SOC significantly. Even assuming that your reported SOC of 55% is accurate, it only takes about 1/4 amp to draw down a 300 Ah battery bank to 55% in three weeks.

Storing lithium batteries at 50-70% SOC will give you the best life, but you can't just disconnect the battery terminals if you depend on those batteries for the bilge pump. That is one of the dilemmas of using lithium batteries on boats.

Since you probably can't eliminate the 1/4 amp parasitic draw, consider adding a small solar panel even a portable one to keep the batteries up while the boat is in storage and live with the reduced battery life. A 100 watt panel, controller and wiring can be put together or less than $150.

David

Hello David, Your statement, "Even assuming that your reported SOC of 55% is accurate, it only takes about 1/4 amp to draw down a 300 Ah battery bank to 55% in three weeks" answers my question. I have Renogy BMS, 3 Bluetooth LifePo 200 amp batts, a 2nd Xantrex BMS (both agreed with SOC 55-56%) and Xantrex 200amp inverter/charger. Thank you for replying.

artfulltune said:

Hello David, Your statement, "Even assuming that your reported SOC of 55% is accurate, it only takes about 1/4 amp to draw down a 300 Ah battery bank to 55% in three weeks" answers my question. I have Renogy BMS, 3 Bluetooth LifePo 200 amp batts, a 2nd Xantrex BMS (both agreed with SOC 55-56%) and Xantrex 200amp inverter/charger. Thank you for replying.

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Are you in an environment where the temps will remain in the allowed range?

artfulltune said:

Hello David, Your statement, "Even assuming that your reported SOC of 55% is accurate, it only takes about 1/4 amp to draw down a 300 Ah battery bank to 55% in three weeks" answers my question. I have Renogy BMS, 3 Bluetooth LifePo 200 amp batts, a 2nd Xantrex BMS (both agreed with SOC 55-56%) and Xantrex 200amp inverter/charger. Thank you for replying.

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A BMS is not the same as a shunt based battery monitor. A BMS infers SOC from the measured battery voltage and is influenced by any amperage draw. A shunt based battery monitor using a Hall effect sensor measures instantaneous amperage draw and integrates that over time to give you real amp hours used and SOC (assuming it is set up with the right battery amp hours).

David

To be pedantic for a moment, shunt based battery monitors are not Hall effect sensed, if they are would be pretty inaccurate. They measure the very small voltage drop across the very small resistance of the shunt.

One issue with LFP batteries (and particularly the Bluetooth connected ones) is that there is a small parasitic draw even if the terminals are disconnected. This is the power to run the BMS and Bluetooth radio. Some are better at this than others and draw less power, but they all do it. Also, some of them (maybe most) do not account for this draw in their own SOC calculation.

artfulltune said:

Began Haven’s first winter storage in the water last month. Went to check the state of charge and the battery monitor read 56% with the battery terminals reading 12.4 volts, each of the 3 batteries. I leave the battery switch on with all DC breaker switches off except the 3 bilge pumps. The bilges are dry. I turned on the inverter/charger which quickly (1/2 hour) brought the monitors back to 100% with each battery reading 13.32 volts. My question; is 56% SOC normal after 3 weeks with virtually no draw?

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No, that's not normal.
Assuming no draw, You should still be at 100% or very near full.

Something is drawing down your battery. Unless your bilges have been coming on all the time you were away.

By comparison, I have 400A of lithium batts that I remove for winter storage.(2 100A and one 200A) I have not yet put them into storage state (I've been too busy lately) but I just checked them and they read 95% charge. That is after sitting for 2 months (Hauled out Sept 27). There is no way yours would read 56% after 3 weeks unless
a) you have phantom loads
b) your bilges are running a lot
c) You have a defective cell(s) in your battery

DDW said:

To be pedantic for a moment, shunt based battery monitors are not Hall effect sensed, if they are would be pretty inaccurate. They measure the very small voltage drop across the very small resistance of the shunt.

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You are quite right and I know better. My 76 YO mind had clamp on ammeters in mind when I said that shunts are Hall effect based.

David

Hello to All Replying to My Inquiry. Even though I know the 3 House Batteries are Bluetooth enabled, I reckon I forgot that Bluetooth requires some voltage draw that I may have experienced recently. The thing I didn’t do on my last visit was to get the Bluetooth read-out which I’ll do on the next visit. BTW, David, the Renogy Monitor I installed is shunt based. Thanks again.

twistedtree said:

Are you in an environment where the temps will remain in the allowed range?

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Great point. I just installed LifePo4 batteries and I have been told by multiple people that cold temps are what kills these batteries.

Mac2 said:

Great point. I just installed LifePo4 batteries and I have been told by multiple people that cold temps are what kills these batteries.

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Just check what the manufacturer calls for. Do you keep your boat heated at least to some minimal level?

twistedtree said:

Just check what the manufacturer calls for. Do you keep your boat heated at least to some minimal level?

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For sure. I heat my engine room to around 65F. My manufacturer says storage temps should be "temperate". I just wanted the OP to be aware of the cold temp dangers, which I assumed you were eluding to.

If you charge them at cold temps, it will do them no good. Most I have seen are OK being stored at pretty cold temps.

Mac2 said:

For sure. I heat my engine room to around 65F. My manufacturer says storage temps should be "temperate". I just wanted the OP to be aware of the cold temp dangers, which I assumed you were eluding to.

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Yes, that's what I was thinking of. LPF batteries have limits on charging and discharging below 0C/32F.

DDW said:

If you charge them at cold temps, it will do them no good. Most I have seen are OK being stored at pretty cold temps.

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Good point. Use temps and storage temp ranges are different.

If you don't have one then get yourself a clamp on ammeter. Blue Seas offers this one which can read down to 10mA. and seems to be a decent all round unit.

https://www.bluesea.com/products/8110/Mini_Clamp_Multimeter_-_AC_DC

Last year I bought a Klein CL 390 meter which is quite similar. https://www.bluesea.com/products/8110/Mini_Clamp_Multimeter_-_AC_DC

Or borrow a friend with one of them and ask him to help or loan it to you.

Either one will tell you what the actual draw is when stuff is supposedly shut off.
I have been through this with parasitic draws although long enough ago that the draws were no where near where they can be these days but I still had to chase it down because my batteries were no where what they are now.

Many devices do NOT truly shut off unless the battery sw. or fuse/C.B. cuts off the power completely.

-VHF radios, stereo systems, radars, sounders, GPS's, inverters/chargers, USB chargers, a BMS . Almost any device where all you do is push and hold a button has some circuitry operational to sense that push. Not all but.

I am sure there are other devices that do not truly shut off unless you physically pull the fuse or trip the breaker.

Many of these devices won't draw much but a bunch of them together can actually pull quite a bit.
My 4 yr radar will draw 0.8aA with out a turn off sw. which I did.

But a decent ammeter can be a huge help.

There is another way and that is to use a DMM with a the ability to read DC current. THey are almost always limited to 10A but that should be enough.
Just disconnect the batteries, and shut off the loads. Then start reading fro draws. Of course you will still have to chase down all those items individually to find out which ones are still somewhat alive. Usually pulling fuses or tripping breakers.

Hello C lectric – I do own a clamp on which I’ve used for AC loads. Don’t recall the brand. Didn’t think to use it on the recent visit. I was relying on the monitors to show loads but will use it on next visit. Thanks for replying.

artfulltune said:

Hello C lectric – I do own a clamp on which I’ve used for AC loads. Don’t recall the brand. Didn’t think to use it on the recent visit. I was relying on the monitors to show loads but will use it on next visit. Thanks for replying.

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Your clamp on meter may not work on DC loads. An AC clamp on meter uses a cheaper magnetic induction coil sensor that won’t read DC. DC/AC clamp on meters use a Hall effect sensor for DC and a coil sensor for AC.

David

And many clamp on meter that read DC will not read low currents in the milliamps range. Read the specs before buying.

Both DavidM and Headed to Texas are correct.

If your meter does not say , instruction booklet OR on the meter,
Hall Effect for DC and TRMS for AC then your meter , although usefull, has limited usefullness on a boat.

That is why I suggested those two meters. They are decent quality meters and they are not budget breakers, especially the Klien. Yet they can read down to 10mA in BOTH AC & DC. However I do not totally trust them at this level but the readings are good enough that they tell me what I need to know.

THere are other meters that can read current down to 1mA but the price goes up substantially or the range and adaptability for other uses goes down substantially, specialization. Judging by my own experience with these meters at these levels, readings have to be done very carefully as good or not I have found they have trouble making up their mind sometimes. How they are held can make a difference.

There are a lot of meters out there that although decent for AC CANNOT read DC.

I will add that on the DC readings they can tell the polarity of the current. I used that to tell me one battery of my three HOUSE units had become a load to the other two. You just have to be carefull where the meter is pointed, ie: is the meter facing the POS or the NEG terminal.

I was an electrician with some electronics background so used them in my work so have some familiarity with these meters.

Just an add on about your meter loads. Your monitors themselves draw current from the batteries even though the batt. sw. may be OFF. I doubt this draw is taken into account.

I think a 10 ma DC clamp meter is essential on a boat. 1 ma may be occasionally useful but the tradeoff is usually the upper end of a 1 ma meter may be only 20 or 40 A and you'd like to measure more than that on occasion (also they are more expensive). I have a few of these and the one with the smallest clamp jaws is most useful (from Extech). It is rare that the jaws won't go around a wire you want to measure, more common that you have trouble getting it into and around what you are trying to measure.

Storage of LiFePO4 batteries below freezing or operation is not a problem.

Just don't charge them under 32F

Delta Riverat said:

Storage of LiFePO4 batteries below freezing or operation is not a problem.

Just don't charge them under 32F

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It's true that temperature is more restrictive for charging vs storage and discharging, but the storage and discharge temp isn't unlimited, so worth a read of the data sheet.

TT
Do far north (or south) off the grid home and business Li battery users maintain a heated battery “house”?

sunchaser said:

TT
Do far north (or south) off the grid home and business Li battery users maintain a heated battery “house”?

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I think most live in the house somewhere, so have a controlled temp range. Mine are in the basement which never sees less than 50F, or more than 70F. The same is true for boats that remain heated. We leave our heat set to 50F when away, and that keeps the laz where the batteries are in the 50F range. It's not heated space, but there is heat thrown off from the boiler that keeps the space comfortable.


I think temps are only an issue for unheated boats, and boats hauled and put up for the winter in cold climates. Most boats in New England, for example, get hauled and blocked outside for the winter. That will put the batteries into a range where temps are a consideration.


I suspect high temps are the bigger issue for anyone upgrading to LFP because a lot of lead battery banks are located in engine rooms or engine compartments. The space would have to be carefully checked to be sure the actual battery location will experience acceptable temps. Low down in the space, which is a common location, may be just fine, but it should be confirmed during a long run.

twistedtree said:

I think temps are only an issue for unheated boats, and boats hauled and put up for the winter in cold climates. Most boats in New England, for example, get hauled and blocked outside for the winter. That will put the batteries into a range where temps are a consideration.

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Exactly. Winter storage is the one big point of temperature concern I have with LFP. It would be one thing if I didn't touch the boat all winter, but it would take some extra preparation to handle the scenario of the boat sitting in below-freezing weather on land, but with me occasionally going to do some work on it and plugging into power while I'm there. I'd have to set things up such that the house batteries could be isolated and have an alternate source of house power (or have a way to heat the batteries and then charge them). Just cutting off charging in the cold wouldn't work, as I'd end up drawing down the batteries instead.

Quite a few LFP battery makers are incorporating heaters into their batteries to offset cold weather issues.

https://battlebornbatteries.com/heated-bb10012-battery-is-now-available/

Peter

rslifkin said:

Exactly. Winter storage is the one big point of temperature concern I have with LFP. It would be one thing if I didn't touch the boat all winter, but it would take some extra preparation to handle the scenario of the boat sitting in below-freezing weather on land, but with me occasionally going to do some work on it and plugging into power while I'm there. I'd have to set things up such that the house batteries could be isolated and have an alternate source of house power (or have a way to heat the batteries and then charge them). Just cutting off charging in the cold wouldn't work, as I'd end up drawing down the batteries instead.

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What you describe is exactly how I "used" my boats when they were hauled over the winter. A shrink wrapped boat actually isn't too bad a place to work in the winter, and you can get a lot of projects done.


I think in that situation the best approach is to completely disconnect the LFP batteries and switch to the start battery bank. This requires a parallel switch, but not too hard to add, and arguably a good backup for power in case of an unexpected BMS disconnect. It also assumes both banks are the same voltage, which I think is true more often than not. And if temps will drop below the allowed storage temp for the batteries, remove them to a warmer storage location. I know I wouldn't want to do have to do that, but if you must then you must.

If your in the water , Why is the battery charger turned off? Isn't the boat plugged in to shore power?