Battery settling voltages. What is acceptable?

[Steve_S]

Thought I would chime in for a moment.
Having done a LOT of testing on various cells, even hard core nasty Thrash Tests (controlled abuse) I can tell you that with LFP you can charge & saturate cells at 3.600 or 3.650 till they take <0.5A. Within 4 hours they will show around 3.55V and after 12 hours will likely be sitting between 3.450-3.500 and they will pretty much level off there +/- 0.050. Now this is with Standard Prismatic "Square" cells. Most LFP, even Cylindrical will do very similar, it is the chemistry. One exception in LFP Land, is cells which are Yttrium Doped or special purpose chemistries (which there are a few) and these are not used for ESS (Energy Storage Systems) due to cost.

Here is a quick Voltage Chart for LFP which may help answer a few things as well.
BTW: More "Commercial/Retail" assembled battery packs of "reasonable quality" will NEVER allow a cell to reach 3.65 or drop to 2.50 volts, their BMS' will cutoff and limit the charge/discharge to maximize lifecycles. The Main Powercurve for LFP is between 3.000-3.450 volts with the nominal power rate at 3.200. It is not unusual to see Commercial Batteries cap at 3.450 at the top and 2.750 at the bottom but "some" will go the full 2.500-3.650, those I would hesitate with unless I was certain the SCC & Inverter system could actually perform proper cutoffs and act appropriately for the battery pack(s). This is complicated if more than one battery pack is in a battery bank.

Hope it helps.

 

[Repro]

Thanks for the input. I have continued to monitor the voltages every 12 hours, and the suspect battery has settled at 12.86V, the other three batteries are still discharging, but very very slowly, and they have the same voltage of 13.65V. I am going to give this a week and give Lion Energy the recorded data to see what they say. These batteries are only about a year old, and they have lost some of their spunk. They have been kept in a climatized environment, and only cycled maybe 12 to 15 times. Thank again.

 

[David G]

I have a slightly different issue with 3 new Lion Energy Safari 1300 batteries. I charged each battery separately using a Victron Smart 17 A charger. After an overnight rest two of them showed 13.47 +/- 0.04 V and the other battery was at 14.3 V. I discharged the offending battery and this time it settled in at ~13.49 V but after 24 hours the V was 13.91, a difference of 0.4 V. A measured voltages with a Fluke multimeter at the terminals. I had a coulomb meter attached and it verified the voltages and the charger profile.

Lion Energy was helping via text messages and asked for me to discharge the offending battery to 'exercise' its BMS. I need to get back to them but first I wanted to hear what others say about this battery behavior. Should I just ignore it and install the 3rd battery or pursue it with Lion Energy?

BTW- I'm new to this forum and it is great! I'm really learning a lot as I install my 600 W solar system with Victron 12 3000 W Multi-plus inverter system on my travel trailer.

David

 

[Repro]

I forgot to post about my Lion Energy battery as I am dealing with other issues at the moment. Lion Energy communicated with me per text as well. These four Lion Energy batteries did not get much use since last summer. They told my to discharge and recharge all of the batteries independently. I did so again and again, and the offending battery still settles lower than the other three batteries, but the continuous discharge like before is not near as bad. I am going to start using them again in May regularly, and I will see what happens. The warranty is still good for a long time. Lion Energy commented that leaving the batteries unused and connected (four in my case) in parallel or series for a long periods of time shoud be avoided. If they sit, disconnect them and leave them sit indepedent of each other.

Glad it worked out for you as well. Welcome to the forum!

 

[Pres]

"......Lion Energy commented that leaving the batteries unused and connected (four in my case) in parallel or series for a long periods of time shoud be avoided. If they sit, disconnect them and leave them sit indepedent of each other."

Good tidbit of info here, thanks. I will keep it in mind for the two that I'm installing in my camper. I paralleled mine with 1/8" x 3/4" copper bars (good for approx. 215A) and it's an easy one bolt removal.