My focus for the past few months has been with NiMh batteries. Although they have a high power capacity of around 2200ma they only produce around 1.2 volts as compared to lithium or alkaline batteries which produce 1.5 volts but at a reduced power capacity for alkaline and an increased cost for lithium. I've discovered that, when powering my iPod with a two battery external power adapter, if the voltage drops much at all the iPod complains that the device cannot be used for charging and then uses its own internal battery.
I have two solutions right now; one is to use the two battery iPod unit with freshly charged batteries (seems like a lot of work) the other is to use the 4 battery unit with the iPod USB cable.
