Question: I have received a shipment of LFP cells from you company. When I received them, the voltage was about 3.25V for each cell. Now the voltage is below 3.10 for some cells and some have even just 3.0V or even less. Why is this so?
It is important to realize that cells shipped from GWL have only a partial capacity.
The DG cargo safety regulation limits the maximal permitted charge to a value below 30% of SOC. In really it means that the cells have less than 30% of the SOC.
RECHARGE: When you receive the cells, you should check the shipment first and charge the cells to full capacity as soon as possible. If you leave the cells unattended the cells continue to self-discharge.
The average self-discharge for LFP cells is between 3% to 4% per year. This means that fully charged LFP cells will stay with energy for many consecutive months. However, the self-discharge rate increases in some conditions:
The self-discharge will increase for the cells that are nearly empty. These cells may self-discharge as much as several amps in during a few weeks. The empty cells self-discharge quickly.
Also, the self-discharge rate will increase when the cells are subjected to changing conditions. For example, if the cells are stored in warehouse with no significant changes of temperature, the discharge cells will not change.
However, if the cells are taken form the warehouse and shipped to customer, they will be subjected to changing conditions — temperature changes, the change of the position during transportation, etc. This will result into an increase of the self-discharge, especially in cases when the cells themselves are already nearly empty.
Summary: be sure that you charge the cells quickly after you receive them from the delivery, do not wait until the self-discharge will increase and the cells will get too empty.