Disk arrays on servers usually have an acceleration unit with memory and a battery to prevent data loss in the event that there is a black-out.
Since the Ni-MH array accelerator many HP servers work with 3.6V (three 1.2V rechargeable batteries in series) is replaced by a single Li-ion protected working between 3 and 4 battery , 2V (at 3.6V is 40% capacity).
The original battery, spare ref. 307132-001 HP is 500mAh, so a Li-ion 2600 mAh far exceeds that capacity, so it will retain more energy and for more years than the original having no "memory effect" (probably last longer the server itself), protecting better against unexpected power outages data (also recommended a UPS).