How much words can a pen with half refill write?

Question

We start with what a pen can write, Then add an "s" for a tool of lesser might.
Change "d" to "n" for an oath professed, Remove letter one for a condition no longer the best.
Change "w" to "t" for something forced apart, Reverse my ends, then add an "h" for what's atop a chart.
Change "n" to "w" to learn how much an item can fetch, finally, anagram me for what in baseball may follow a stretch.
What did we start with? What do we end up with?

Answer 1

A pen cannot write even a single world. Its the person holding the pen who can write the words.

Answer 2

half as many as a full refill can