ORIGINAL: HighPlains
voltage is not important is starting, its amperage
Not really true. You can not increase the current that the motor receives until you increase the voltage to the motor. What is true is that different batteries have different internal resistances which drop the open circuit voltage of the source when under load. The speed of the motor is proportional to the voltage applied, but the power of the starter is proportional to the voltage applied to it squared.
So you want more voltage and a low internal resistance in the battery.
well you need some voltage or you arnt going to spin the starter at any decent rpm, but what a lot of people overlook is that their batteries cant deliver the amps needed to turn over bigger engines,
to my understanding
voltage controls the rpm of the motor/starter
amps control the amount of resistance that the motor can take at a certain voltage
for example i can start 40 sized engine on a 6 cell, 7.2v, nimh high current pack. this is due to the fact the starter can draw a ton of amps from the battery
i then tried a 14.4 old drill battery pack when i was starting .91 sized engines, it couldnt turn it over (or the .40 sized) because it couldnt deliver the amps needed, it would spin the starter like a top but once you applied some resistance it stopped rather quick.
now if you want to increase the power of the starter you may need to increase the volts, but dont bother increasing the volts until you maxed out the amps aka try a car battery if that doesnt work go to a 5 or 6 cel lipo, or 2 deep discharge batteries.
make sure your battery contacts are clean or your wasteing your time w/ the car battery.
some starters arnt strong enough so you will need to buy a bigger/better one, but a lot of the time it is the battery