That does look like a neat gadget.

You could always rig up mulitple batteries in parallel for longer runtime, just like with a troller. Just have to match the voltage of the bulb.
The rectangluar ones are 9 volts, asJudd said, and the pack of 4 AA's together would be 6 volts.

So they either have a new 6 volt light, or they are running the original 9 volt light at 2/3rds the power. It's OK to run an incandescent light at lower voltage. You just get lower light output. The tradeoff in linear though. You can't get bright light AND longer run times just by changingbulbs or batteries.

Rechargeable batts might keep their brightness longer, but they tend torun out quick once they start to get low. Instead of a gradual degradation in current output, they go great right up until they are just about to go dark. Might be better if you just bring some spares.
Ask Eddie if he would expect any problem with rechargeables.