At this point the core of the bud is composed of the motherboard, a big battery, and a plastic cup that probably helps with the physiscs of the sound but (being glued) will never go back quite correctly in place.

Prying the core we finally observe something that is not glued. The battery is a Lithium Polymer 1054 soldered in place (of course). Assuming that somehow you managed to get to this point without destroying everything, desoldering the old battery and re-soldering a new one should be quite feasible.

It looks to me that it would be safer and faster to operate directly on the motherboard to replace the battery.

Moving back to the stem. It is completely glued. The only way i can conceive to get to that doughterboard is to slice through the entire stem, which would not be really economically feasible.

In conclusion these earbuds are completely at "Apple Levels" of unserviceability and irrepareability so, if I can dare to give a score, they would score a 1/10 iFixit repairability score.

They are not scoring zero because if the shell wasn't so stupidly build several components could be replaced.

I dare to say that if somehow they did not have glue, and if the daughterboard was accessible, they could score a lot higher (maybe 6 or 7), because at that point you could conceive to replace the speaker, the battery, the motherboard, the plastic cup, the daughter board, and the shell with minimal additional equipment.