Is the M-241 so battery demanding?
That’s crazy. With backlight off but showing a map a Vista HCx on 2 AA eneloops gets about 25 hours, while showing OSM maps and mtbiking and recording tracks to microSD. Even with backlight on at 100% you get 12-13 hours. The 60CSx gets about 30% shorter times (maybe less difference with full backlight, which is not as light as the one from the Etrex series though).