Here ya go. Location of the PF. Battery to right. My _bet_ is it lifts right up and out (slide to right?) and is held in place by a friction fit.
I haven't done it but it, barring some BS snag which I DOUBT is there, it looks like a very easy DIY.
BTW, housing is not a diagrammatic "cutaway" like I speculated, it actually looks like that; made of closed-cell foam (very flimsy/fragile).