Hi Ted,
yes i did pictures, but had no succes in uploading here (needing help).
soldering is easy. cut the cables off near the batt., do two big soldering drops on the fp120 + and - contacts in good distance from open mr1 (it's a quite normal no name fp120 for fuji and others around 5$). measure the two cables from mr1 batt to define the + - poles. the fp120 has 3 contacts. ignore the middle position. the black mr1 cable goes to the outside contact of the fp120, the red mr1 cable to the third fp120 contact positioned not direct on the other outside. so it's mine (measure it yourself). fill the empty space in the mr1 housing with two folded pieces of allround kitchen cleaning paper to avoid electric contact and batt. rumbling in the moved machine. the fp120 has like other camera batts an inbuilt power management system defining loading and working limits. the mr1 loads it and works it down after that system. think You can take every other 3,7v managed batt, it's a question of size.
*** think it's worth looking for a good running and not oversized ext. batt. solution. the inward batt runs for shorter takes and remains necessary for all ext. solutions because both power entrances (usb, ac) aren't saved against interruption like the hirose connected pro gear, sd, sqn and others; but they all are much much bigger; and the mr1 entrances are more professional defined as the small nagras. if you use good or better portable preamps you don't need the doubles in the big bags. and if you can't pay smiling guys carring it, than mr1 is unbeatable and a really necessary starting a possible future layout; no 3,5mm jack per se is kidish, but every stereo jack. ***
some words to the mtron. i think, Ted, its good running with mr1 is (YOUR) great observation. one of mine mr1 hitachi hds did writing tickle noisy hearable in a circle of 2m around the mics. i need essentially an organic silence in the recording and the monitoring haedphones. trickle trickle, Korg didn't select the hds. in one is a quiet hd, other plays with fingernails on the desk. another single bought exchangement zip hitachi sounded above 6 khz like a small intriguing bagpipe, and the zip hds are going out like the zip mlrs, so the price for mine (used) mtron 32gb mlr went down year ago to 42 €.
and the ssd works nearly elegant. starts and shuts tree times faster, copies fastest. gives a better feeling in hands, especially in the field. runs with all formats till it's full, mtron is more long time reliable (if for 100 years i hope to experience it).
in long lasting field work i wrote it full. easy rule: never delete tracks from portable devices, to risk no fragmentation. when it's necessary, format it. every morning formating comes from older times small media capacities and from craftsmen religion. a newly formated disk is not "empty" like an unexposed film.
who can show us a newer small sized device with pro ad conversion (pcm is excellent too on mr1) and balanced line ins, yes, remember: two balanced mono 3,5mm line ins, two mono with choosable 3v plugin power feeding p.e. two mono dpas for who likes it minimized?? such an extreme solution today? who did it before?
remaining - encore - mr1 batt desaster.