starter motors draw so much current that any other circuits will have its share of the battery leeched.

The best suppression for starter motors I found were the drive mechanism from a circuit breaker - if you take one apart there is a set of copper plates with air gaps - connect both motor contacts to the 2 outer plates.

Also, to diminish the amount of current the motor wants to take, allow the motor to rev in excess of 10,000rpm - by the use of gearing - and it will not only speed up very quickly but generate a lot of internal resistance, hence reducing current flow.