I have never known anything but AA's, my "go to guy" in the camera shop up in the city put me on to some super re-chargeables...
Sorry to have used Home Depot but first one came up in search (on dialup today
I have a couple sets of these and a "smart charger" I can use in my vehicle (any 12V plugin) or at home.
Two charged sets of these and I don't think there is enough daylight in a day to run them down.
I don't do alot of flash shots so I can't speak for that.
That though, brings up my wish....a taller built in flash.
I constantly get the shadow in the bottom of my frame using the 18-55mm kit lens,hood on or off.
The flash is plenty strong enough for my use.
I think they could have made the actual bulb part of it slightly adjustable so one could "fix' that by just tilting it a degree or two up or more even to give a bounce flash kind of.
Can't see that being rocket science really and how handy would that be?
Faster AF and maybe a few more but not many FPS for birds in flight.
Pentax 18-55mm,Pentax 50-200mm,Sigma 17-70mm,Sigma 70-300mm, Sigma 50-500mm