If the battery needs new cells the have it re - celled by BGA Reworking/ebikebatteries.co.uk based in North London.
The battery code comes up as a Phylion case battery.
Finding the exact case type you will need to enter Phyion XH259-10J in to search sites to sift through them looking for one but as I mentioned if it is because of cell aging or lack of performance then have it re-celled.