At a quick glance the hardware for this is compatible with Lithium Ion chemistry so go for it. Just need to make some minor mods to put a battery holder on. Mo

At a quick glance the hardware for this is compatible with Lithium Ion chemistry so go for it. Just need to make some minor mods to put a battery holder on. More specifically, just about any headphone with a LiPo (flat square) battery could be modified to accept an 18650. The charging voltages are the same, so you would just have to snip the old battery out and wire in an 18650.