I just tried with mine - I have problem with actual earbud's battery - it does not last long anymore.
It's not hard, but you should be careful. The insides are glued together, but I was able to open it just with my finger nail.
Afterwards, you unplug the pin and push board up. Better start doing it by pushing charger pads with a something thin, to avoid breaking them (that what happened to me, however should be easy to solder them back).
Battery itself has marking 0.196WH Li-ion VDL 1240H, however I was not able to find exact substitute, will try some other battery of a similar size e.g. LIR 1240.
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