We need to know why the train/mp3 player do so badly with Batteriser.
If we take the amount of energy needed to get the train around the track as our unit of measure then the Batteriser is only about 60% efficient.
That's a plausible figure when you're working with low voltages and tiny components but is it really that bad after all the hype we've seen? No wonder Bob has been trying to keep them away from engineers.
There is likely to be a signficant reduction in the efficiency of the train as well as the voltage increases! Small, cheap, brushed motors have terrible hysteretic iron losses, that increases rapidly with motor speed. It's not unusual to see a 15% reduction in efficiency from just a 5% "Overspeed"
One test that would be interesting would be to power the train with Daves Lab PSU (using a pair of long wires to allow it to continue to loop round the track a few times before getting twisted up!) and record the power consumption at various supply voltages!
The biggest irony is that because batteries are electrochemical, ie, the movement of Ions within the compounds of the battery create the electron flow, this is a electromechanical process and hence it is "rate" dependent. Pull lots of electrons (high current) from the battery, and there is simply not enough time for Brownian motion to stir the chemicals to provide enough ions, so the battery goes "flat" (ie, output voltage falls). The Bateroo, being a boost convertor, actually loads the battery with a higher average current (on a passive load) and so requires a higher rate of ionic movement, and hence actually renders a proportion of the electrochemical energy un-useable! From the train test, it looks like, for a typical AAA battery, that un-useable proportion is larger than the un-used (due to insufficient voltage) portion without the Bateroo.....
What we would need to see if the discharge curves for these batteries at a range of different discharge rates. In all cases, i'd expect the lowest possible discharge rate to be able to extract the largest total energy from the battery.