You can never have enough batteries. Spares for the camera, the strobes, audio recorder, etc., etc. I add batteries to every shopping list so I’m not caught unprepared. When I see a battery caddy half-empty (it’s never “half full”) it’s a warning sign.
Time to stock up.
As for rechargeables, keep ‘em charged and have a rotating system. A good battery checker is a helpful accessory. When you head out on location you don’t want half-drained bats loaded. And if you’re shooting video with a DSLR, twenty minutes of shooting will drain the power. Pack spares.
So how many batteries do you have on hand?