having made the mistake of trying to get to much time out of my rechargeables in my sbm-1 one too many times, i now carry an extra set of 4 rechargables AA's and change at an appropriate time...ie set break.
i do not like to see the sbm-1 go under 3 blips with the rechargeables, cause you aint got long on 2 blips before you are dead. two blips seems to turn into one blip real fast...at least this is my experience
conversely, my d8 lasts 5hrs easy with one set of (4) aa rechargeables. i guess the motors on the d8 do not suck up as much juice as the sbm-1 which has to a/c and dither to 16bit.