Another problem is that the display also eats juice. Ideally you'd want to run with the display off as much as possible to give best battery life...

It doesn't last long with alkalines, I have tried this once. You really need Nicads/NiMH/Lead-acids due to the current peaks. Bear in mind, though, that it was never designed to be a battery operated device and so isn't terribly frugal (ie, the display filament heater takes over a watt alone!)

Hugo