I'm paranoid about an atty dying or being out with a dead battery, or not having juice, or the sky falling (not really). I used to have chargers at work, a car charger, carry spare everything. I simplified it. I carry 4 or 5 filled cartos, a couple of 1 dram eyedropper bottles of juice, and go ahead and put batteries in a couple of mods.
Found a few aluminum cases, for ipod or something, on clearance at Wally World for a buck each. Got all they had. I can go all day, no sweat.
Rocket