A rechargeable battery, like any brand battery, has an expiry date. For most products, this is printed on the cell and usually lasts between 10 and 12 years from manufacture. With special batteries, it is unfortunately not always possible to look at the cell to check the date. In general, I advise against buying batteries in stock because you may not need them for several years. Since you never know how full the manufacturers' warehouses are, it can happen that the batteries have been in storage for several months or even years. Since today the delivery of a product usually takes place within a week and the batteries of the APC UPS, for example, will easily last a few weeks even when the battery capacity of the device is reported, I would not buy batteries as a reserve. In the case of the APC, it reports the warning relatively early so that you have time to get new ones. At most, the UPS support may be a few minutes shorter than with new batteries. By the way, the expiry date always refers to an unused cell.
