This idea that the Rcexl ignition can not handle voltages above 6 volts is just wrong. If that were true everyone would have to be using a 4.8 volt pack for ignition.

What they are saying is don't use voltages higher than you would get from a 6 volt pack. A fully charged NIMH 5 cell pack is actually about 7 volts and comes down gradually as it discharges. By the time you get to 6.0 volts the pack is almost fully discharged.

An A123 pack has 6.6 volts normally and 7.2 when fully charged. It comes down from 7.2 to 6.6 very quickly. 6,6 is well within the operating range of the Rcexl ignition as long as the ignition has a date code of 2008 or later. If your ignition was made before 2008 then stick to a 4 cell pack or use a 5 volt regulator.

TF