So let's say I use three AA batteries instead of two, giving me 4.5 V.

I can put the 4.5 V straight into the PIC without a problem.

Should I use the 4.5 V to power the driver chips?

As people have already mentioned, the driver chips I'm using have 
darlingtons inside them, so I'm wasting power. Would I be better to 
replace the driver chips with individual transistors? If so can someone 
suggest suitable through-hole transistors to use? MOSFET's maybe?

Or perhaps is there a driver chip out there that doesn't waste so much 
power?

Does anyone know approximate average values for the milliampere hours of 
AA and AAA batteries? I've looked at a few datasheets but strangely most 
of them don't mention it... and for the few that do mention it, there 
seems to be massive variation (e.g. from 500 mAh to 2.7 Ah).

I went to the Duracell website (they're a popular brand of battery in my 
country) and I still couldn't find out what the capacity was of their AA 
and AAA batteries.





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