How Long can LiFeP4 batteries sit with no charge?

JustPractical

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I purchased four 48V 100AH LiFePower4 Battery by EG4 batteries that I received in January. My plan was to wire each individually to my GroWatt inverter and charge them off grid, and then once i had done that for all 4 individually, I owuld wire them all up in parallel, and conenct them permanently. This is to avoid having to purchase a seperate charger, while still allowing me to balance them off.
Two quetions:
1) How long can the batteries sit in their box not being charged before tehy become damaged in some way?
2) Does the above plan sound reasonable for initial charge?
 

rickst29

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Answer 1: It will depend on power consumption by the BMS (if active). The cells themselves loose less than 1% SOC per month (at room temperature, they lose power more quickly at higher temperatures). So, if they were sent to you at 30% SOC or higher, which is typical for LFP battery pack shipments, your 5 months (plus some storage time in a warehouse) will be insignificant - until we consider the on-board BMS.

If it doesn't shut down automatically after a long period of inactivity, and was not shut down at the factory (pending re-activation by a future "charging" situation), the BMS itself could be consuming a lot more power than the idle cell loss figure. But I'd be surprised by use of a BMS which doesn't shut down according to an idle timer - most brands have a default timer of around 14 days.

So your plan sounds very reasonable, unless "EG4 batteries" did something unusual/bad.
 

JustPractical

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Rick - Thanks for the info. With the BMS built into the battery chassis, you think it's safe to assume if the breaker on the battery is off, then the BMS is "off"?
 

400bird

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Nope, my opinion is not that is not a safe assumption.
I'd open it up and unplug the BMS. Or check the cell voltage weekly and recharge when needed.
 

Borneoboy

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Be careful though, I left my Heyo "smart" BMS attached to my battery pack for a week or so while awaiting other solar panels and it drained all the cells, some below 2.5v and one down to 1.6v, from which it never recovered - NOT very smart.
 

rickst29

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Be careful though, I left my Heyo "smart" BMS attached to my battery pack for a week or so while awaiting other solar panels and it drained all the cells, some below 2.5v and one down to 1.6v, from which it never recovered - NOT very smart.
That's bizarre and IMO a BMS defect, if truly caused by the BMS alone (with no external "phantom loads" pulling out considerable but unmeasured battery power). Idle power consumption of the good BMS units is only a couple of watts while Bluetooth is not actively connected: If the cells were larger than 60Ah each and combined into a pack of at least 4 cells, AND it started out near 100% SOC, then it should have lasted longer than a week - even at fairly high power consumption of 3-4 watts.

Quick and dirty calculation:60 Ah * 12.8 volts combined delivery voltage = 768 watt-hours of nominal capacity. Reserving the bottom 10% for low voltage safety, you've got about 700 watt-hours usable in that theoretical battery pack. 700 watt-hours / 3 watts = 233 hours, more than 9 days. But this quick and dirty calculation does imply that your BMS could have "burned down" a small battery pack in that time frame, and could even do it more quickly in the cases of higher BMS power consumption or lower starting SOC. Your BMS failed to shut itself off due to low voltage, and I consider that to be a defect in its design and implementation.

My own minimum voltage (lowest cell) is set at 2.899 volts - and if I could modify that to be even higher, I would do that. (I feel that the common default value of 2.50V is a really bad minimum voltage number for LFP cells.)
 

Prince Of Darkness

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A couple of comments;

Recently received a few EG4 LL, 48 V 100 Ah batteries. On each of these, the BMS was off/hybernating. The SOC of each of these batts, was 52%.

The spec for BMS self-consumption for the LLs, is 14 mA when actively charging/discharging, and less than 300 uA for sleeping BMSes.

Slightly different battery, than the OP's, just FYI. POD.
 

rickst29

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A couple of comments;

Recently received a few EG4 LL, 48 V 100 Ah batteries. On each of these, the BMS was off/hybernating. The SOC of each of these batts, was 52%.

The spec for BMS self-consumption for the LLs, is 14 mA when actively charging/discharging, and less than 300 uA for sleeping BMSes.

Slightly different battery, than the OP's, just FYI. POD.
Yep, that's only 0.7 watts in active use. My calculation assumed BMS power consumption which was 7x worse than the specs on your BMS. We could actually find the number, I suppose, by putting different coulomb counters on both the "P-" versus "B-" leads, and checking out the difference under various levels of charge/discharge, with and without monitoring.
 

Borneoboy

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It wasn't on my current setup but on a new project. So not sure what the SOC of that new 100 A/hr barrery pack was, probably delivery voltage, say 3.2 * 4. This Heyo BMS didn't want to "come on lineĺ unless a charging voltage was applied. Was also very difficult to wake up the Bluetooth connection. I thought it was completely OFF, so imagine my horror when I came back to the project a week or so later and found my batteries completely depleted one of them at 1.6 volts !
I did complain to Heyo company, but they just kept saying "you must have wired it up wrong" and sending me their wiring diagram... that was all the customer help i ever got.
 

rickst29

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That sequence of "support events" definitely sucks. I feel that they should have at least refunded the BMS cost, because it FAILED in a cell-destroying way. :mad:
 
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