http://www.youtube.com/watch?v=IDa-rJxvYV0 I fired this up recently and found it abit strange in the way it lights the tube. I used a 36w T8 fluorescent tube and the battery was almost in an uncharged state assuming the batteries I bought were 'get rid' stock so they were in very low charge state. But this ballast could still light the tube without any purple glow and when I finally fully charged the batteries the brightness of the lamp was just abit brighter. Another odd thing is when I removed the center two connections assuming it is two wire instant start inverter there was purple glow and the tube could not get past the purple glow. Made me think is there preheating? Or some kind of super "energy saver" in there that will keep the tube alight even in the worst battery conditions... The batteries have been configured to give 6v so there are 5 cells per capacity.

Your emergency inverter is probably rapidstart or at least the cathodes gets heating current after starting in a four wire instant start inverter.

Rapidstart, supplies current to the cathodes and to the tube itself at the same time, causes the lamp to initially half of its brightness (But without a blue glow because the cathodes are heated), and then full brightness and the current continue to flow through the cathodes.

Four wires instant start, cold cathodes starting the lamp, but the rest is like a rapidstart (Current heats the electrodes after ignition, not the discharge), so the cathodes still gets the heating current after the starting, but not during ignition. If the lamp have a hard start for a long enough time in this type of ballast, the cathodes may be sufficiently heated during the ignition trys, resulting in a warm starting. Thats also why when the starting capacitor is broken or the lamp lost vaccum, the electrodes glows at the ends even with this type of ballasts.

Two wire instant start, don't heats the cathodes at all, and is like the operation of a preheat magnetic ballast missing the starter (If the lamp starts directly from the mains, as in the case of Tungsram 40W T12 lamps form the 90'), so this results in a cold cathodes operation, a blue end glows and a heavy sputtering, when underdriven.

I haven't tested the full discharge cycle but this thing can run off the batteries for over an hour really amazing. Still no blackening but I have to run it longer to be sure.

So this means that the inverter heats the electrodes during operation.

So this means that the inverter heats the electrodes during operation.

Does not have to. If the lamp goe into the hot electrode mode, then really low power suffice to keep it there.
Yes, the cathodes are degrading a bit faster than at normal power, but on the emergency unit the overall burned hours are very low, so even when the lamp reach the lifetime about 1000 hours, we are talking about decades (in years) of the useful life. And for that ~40W power is sufficient without the external heating.

The problem usually arise when the lamp does not transfer to the hot electrode mode, then the lamp life become even 10 hours and below and that become the real lifetime problem.
And that is, what happen with many inverters: The low ballast power capability into a high voltage drop across the cold cathode operated lamp does not provide enough electrode heat to transfer the lamp into the hot electrode mode and then the life really counts in hours.

And there are circuit tricks to heat up the electrodes when the discharge is not there or the voltage drop is high (no discharge or cold electrode mode), yet do not consume any power on heating when the arc voltage become low (in the hot electrode mode), all that without any active switching element (the trick is, than the filament is in a diagonal of a bridge formed by secondary taps and some capacitors, what is highly unbalanced, so feed the filament with quite high power when the lamp have high drop, but well balanced, so no filament power when the lamp is in the low drop, hot electrode mode).