Out of a test sample of 25 pens, I got the average of 204,8 charge per pen, 5 pens were above 250 charges. Seems a bit silly bod rewards doesn't really have more worth mentioning, or? Test data in "spoiler".
Charges of individual pens.
166
142
194
114
188
134
162
184
168
192
=1644 (10 pens under 200 charges)
238
206
204
206
234
224
214
210
214
234
=2184 (10 pens 200-249 charges)
260
260
258
252
262
=1292 (5 pens 250+ charges)
1644
+2184
+1292
---
5120
5120 / 25 = 204,8 charge/pen average.
166
142
194
114
188
134
162
184
168
192
=1644 (10 pens under 200 charges)
238
206
204
206
234
224
214
210
214
234
=2184 (10 pens 200-249 charges)
260
260
258
252
262
=1292 (5 pens 250+ charges)
1644
+2184
+1292
---
5120
5120 / 25 = 204,8 charge/pen average.