I must admit that I'm surprised that Amazon didn't make the cover battery more like 5000 mAh. A
2500mAh polymer lithium ion battery weighs 52g, so increasing the cover capacity from 1290mAh to 5000mAh would increase the cover weight by about 70g.
5250mAh would (using Erich's smaller figure) give 100 hours of reading time, or over six months at 1/2 hour per day. Now that's a length of time worthy of describing as months, not weeks.