I live in a remote place so the only option was to send it to replace cells (battery contains 4 cells). Cost was around 70 usd here in Argentina.
I've seen that Aliexpress, Amazon and Ebay have replacements, but the shipping was super expensive.
Happened today. Mine stops charging at 61%. Also more or less 2 years old.
Something I've noticed is that the charging light blinks in a strange way, not like it used to.