I am facing a similar problem as the OP of this question where my environment is good, but I feel like my learning is stagnating and I don't have the ability/resources to change positions/quit my job at this time nor am I sure I would want to if I did have the ability to.
The day before yesterday, I was assigned to help fix a problem with an ASP.NET website (which I normally don't work with) that the customer was having and I needed to look up how to implement something. It only took me a couple of minutes to fix the problem and after that I ended up spending about four hours reading more about ASP.NET and implementing some of the exercises from the book. Then I spent another hour reading about networking and configuring routers which may be used when we need to change something in our lab, however, it is highly unlikely I would be the one to do it since we have a person dedicated to that task.
Today I took off work just so I could learn more about configuring networks and to practice on my home network.
Should I be billing the company for the time learning more about ASP.NET even though it is not a common part of my job or should I be charging like 1/2 rate? Is there a certain number of hours that you feel is acceptable to charge the company for time learning something or self-improvement?