I'm no mechanic, but...
Voltage problem, eh? Either the proper voltage is not getting to the starter, or the starter is the problem. My money would be on the latter. How close is it to overhaul?
You can walk the blades backward from now until doomsday and it won't help your problem although the physical exercise certainly will be beneficial for you. The starter turns the N1/compressor, remember. Nothing...and I mean nothing happens in the N2 (to which the MR blades are rumored to be connected) until you get a fire going inside there somewhere (hopefully the engine, not the cabin). And it ain't the FCU of course, because this problem manifests itself long before squirting any kerosene juice into the can with that sparkumplug thingie snapping away.
When it does run, how your trend check? N1 where it ought to be? 93% or so? Compressor rubbin', maybe?