We just did what Ford did and took ours to Kielder,thats sorted the job......
On the voltage front if im testing anything it have the DCC concepts current and voltage meter in circuit,at 28 volts across a 12 volt motor it would be stoke bank for a few seconds i guess but surely some common sence comes into play
Again on the car front we used two batterys in series on the rally stuff across the starter to lower the current and start them better hot on stage.