Hi Michaelo, welcome!
I don't know what CHM format is, but you might be interested in lcd2eink, which is software(?) developed by one of our forum members named Javese. I haven't tried it myself (more lazy than scared) but I understand it copies the image on the LCD screen onto the eink screen. You would have to copy each page in turn, but it might very well save you some battery life:
https://www.mobileread.com/forums/sho...d.php?t=143791
Another possibility is using Calibre for conversion to epub or pdf. I don't know whether Calibre handles CHM, but it works with an amazing number of formats so worth a look.