iFixit documents battery replacement in the right ear cup and separate ear-pad and headband swaps, giving this over-ear model several distinct service paths.
What to check before buying
Battery and power
The AirPods Max battery guide locates the cell in the right ear cup. Short runtime can be addressed through a battery repair rather than assuming the whole headset must be replaced.
External wear parts
Separate iFixit guides cover the removable ear cushions and headband. These are different jobs from opening the powered ear cup, so a used pair with worn pads need not be priced as a battery repair.