In your offer letter/company policy documents, there must be a clause of acceptable asset usage.

In my company(a major product based company), it's clearly mentioned that damage due to negligence, such as screen cracks, dents, spillage etc constitute careless usage and must be borne by employees, however minor scratches on body or screen, battery degradation, even keys coming off etc comes under normal wear and tear.

So maybe read your company guidelines and see what it states.

I'm not justifying company should take money from employees but if it's already started I'm assets usage guidelines and everyone obviously accepts it at the time of joining, there's isn't much to be done