Ear cushions have a straightforward model-specific guide, but the battery guide uses an electronics-level universal-cell substitution rather than an official replacement battery.
What to check before buying
Cushion wear
The NC700 ear-cushion guide covers a model-specific replacement. Cushion fit can affect noise cancellation, making pad condition worth inspecting on a used headset.
Battery limit
The battery guide describes substituting a universal cell and says Bose does not sell a replacement battery for this model. It requires soldering knowledge, a materially different service path from changing cushions.