The low cranking voltage is common due to the high current draw of the starter. Put an Amp Probe around the starter wire or a volt meter on the battery during cranking. The poor performance of the coil is cured as soon as the starter circuit opens. Ignition coils should work down to fairly low battery voltage, should the alternator fail. The controller may shut down first

I have voltage readout on the EM2, and have seen numbers in the 9.xx area when cranking. 

I have the D580 coils.

Al (Not looking good to make it to Copperstate – roads still closed to Ramona airport. Anyone going who would like to take the ‘Rotary Engine’ forums)