I agree with Nealth and disagree with Andy-Mat on this as my own battery has spent its whole life being partially charged back to full and as I said is has now entered its 6th year of service working like it did when it was new after covering 11,900 miles.
How depleted was the battery generally, when you carried out a fresh charge?
How do you treat the battery when charging if I may ask, as that IMHO is the most important part.
I myself have a modified 24 hour timer to switch the mains off when I myself judge it to be fully charged, time wise. That way I cannot forget it.
My last e-bike I bought secondhand, probably about a year old, treated the battery the same and I gave it away after 6 years of usage, with no noticeable loss of capacity, though I did not do any testing in that area. If there was any loss, it had been gradual and not noticeable to me...I rode about 20,000 KMS on that bike....
I mostly did empty to (or close to) full charges....
Not leaving the battery on the charger after its full, is my personal thought that appears to be the single best practice to give the best long term life of the battery.
I will start planning the build of a charger this year to my own spec, to see if that helps in any way at all...Thats the type of project I love, especially the planning.
regards
Andy