Which SOC to store the cells after testing ?
Minimizing calendar aging during storage
For mid-long term storage, lower voltage is better. This reduces calendar aging which deteriorates both capacity and IR.
Cold temperatures also reduce the aging effect. Thus, for cells that are stored for a long time before being reused, a cold (and relatively dry) storage place is recommended.
TODO : add link to study
See
See
IATA
If we want the cells / new packs to be shipped, they should be at < 30% SOC : “To comply with the newest DOT and IATA regulations, you must have the cells discharged to 30% of their capacity before shipping.”
Will we need to ship individual cells? If so, how is the 30% verified? Is 3.70V considered 30% by regulations?
BatteryUniversity recommendations
Great deal of info here:
- No self-discharge below 4.0V
- Exact storage SOC is not important
- OCV is measured after a 90min rest
- Do not use batteries that went under 2.0V. Copper shunts form inside. Cell could work but be more sensitive to mechanical abuse
SOC / voltage for the storage of second life packs
The lower SOC, the better, but not too low though, as we do not want the residual power consumption of the BMS to kill the pack in a few weeks / months.
25-30% seems good?
3.6~3.8 V ? Depends on the cell’s curve. Adapt according to desired storage SOC
Some SOC vs voltage tables here: http://lygte-info.dk/info/BatteryChargePercent UK.html
This table pretty much agrees with our experiment:
It seems like an ideal storage voltage would be 3.6V.
Ideally, at the end of the test, all cells should be ~the same voltage to be ready to be reassembled in new packs.
⇒ We don’t care which SOC? Standardize a voltage for all cells?
Because once the packs are assembled, they are cycled once. We can the charge them to a precise 30%
Tension de stockage ?
Le plus bas semble être le mieux
Pas trop bas car un pack batterie formé avec, équipé d'un BMS, doit tenir x temps sur étagère (courant décharge des BMS Gouach en stdby ?)
20 or 25 % SOC seems good ?