I hope the following question is acceptable here, as it's half WordPress-related and half-business related.
Updating WP regularly is important for security purposes, but it can be time consuming if there are many websites to update and even more if some updates require plugin updates (and in some cases, a plugin ceases to work after WP update which potentially requires a time-consuming solution).
What is the best solution to address this ongoing problem? Should WP regular updates be charged for example? Should it be mentioned in the initial contract?