Originally Posted by Jimski
apart from the fact that a high-capacity battery usually has a higher discharge rate, which in turn pulls a bigger spring.
Just to avoid confusion discharge rate has to do with cell type (2/3 subc etc) and not the capacity alone. There are plenty of high drain large type batteries with <2000mah. However, high cap. cells are generally high drain.
In this particular problem discharge is not the case. Two mini batteries of the same type and manufacture were used. the smaller cap. battery was able to pull with ease. it's the voltage across the resistive motor. whether it's poor contact or bad cells....meh, you'd have to investigate. this just narrows down the posibilities.