I have little experience with the aviation industry besides once having been a student pilot, but I have a fair amount of experience in the medical device industry. If this were a medical device, there would not be a regulatory process specifically for changing batteries, but there would a process for changing anything about the design of the product.
Briefly, that means that a Risk Assessment of the proposed design change must be made, the design change will be controlled (i.e., Requirements, Design, Testing and Reviews of all phases will be performed and properly documented), then the Design Output must be reviewed for correctness and the results may be used to update the initial Risk Assessment if needed.
Similar processes will apply to an airliner, the question is will they be more or less rigorous.
So yeah, changing a critical component is a time consuming and expensive process.
Briefly, that means that a Risk Assessment of the proposed design change must be made, the design change will be controlled (i.e., Requirements, Design, Testing and Reviews of all phases will be performed and properly documented), then the Design Output must be reviewed for correctness and the results may be used to update the initial Risk Assessment if needed.
Similar processes will apply to an airliner, the question is will they be more or less rigorous.
So yeah, changing a critical component is a time consuming and expensive process.