How many pockets have you got?
The question of batteries rarely concerned us in the old film days - at least for the little people. The mechanical shutter and the finger-powered film advance worked pretty well all the time and no electricity was needed. Adding a selenium light meter to the mixture still avoided a battery, but as soon as the CdS and later cells were incorporated and we got electronic shutters and motor drives we started to have to be cagey about on-board electricity.
We started to have to look for 22.5 volt batteries for flash guns...similar ones for Polaroid cameras...D cells for Graflex flash guns...and then a whole raft of cells for the early strobe systems. Victor Hasselblad introduced us to a small blue-coated stack of nickel cadmium cells for one of his cameras and they were NEVER happy batteries.
Well, things are now digital, and batteries are a fact of life. We get lithium-ion cells with every camera we buy and if we are wise we grab an extra one from the accessories rack to go with the new kit. Of course they are re-chargeable items - that is part of the appeal of digital photography - but the amount of juice that any given camera takes is variable factor and sometimes you need more than one battery to have reasonable working time.
A case in point is my own dear little Fujifilm X-10. It works well, but the small battery fitting in it poops out at about 200 shots. If I am going for a full day's shooting at the car show I need to take 3 batteries. If I were a car show shooter with a big Nikon D3, D4, or D5 DSLR I could expect about 2000 shots on one battery and would not need a spare for the day*.
Here is where the user of the big pro DSLR has it over the user of the mirror-less camera in most instances - the battery on the bottom grip of this kind is larger and goes longer - or it repeats the battery in the camera and thus doubles the life. But the whole assembly is heavier, so there we go again with the pros and cons.
That's the new Pentax K-1 in the pictures with the accessory battery grip on the bottom. Well-proportioned for a larger hand and all the controls you could decently want scattered on the top and back. A rumour on another site says a new grip for another camera may well have two batteries plus the one in the camera - 3 altogether - makes lots of electricity but adds extra weight. We'll wait and see if the rumour site is right.
* but I'd take a spare for the day because I am the nervous type.
