What a minefield camera batteries are!
In the good old days, all digital cameras ran off the standard AA battery. You knew where you were with AA batteries and if yours died when you were out you could nip into the nearest shop and pick up a fresh set of batteries. Then camera manufacturers found their cameras consumed so much power that they had to create their own batteries. Of course, these manufacturer special batteries came at a premium price. Instead of $5 for a set of AA alkalines or $10 for a set of AA rechargeables, the new batteries were $40+. A very nice little earner for the camera companies and of course the camera buyer is then locked into buying batteries from that company. 2 is the minimum recommended for a camera and they supply just one.
In the past I have tried knock-off batteries from manufacturers other than the camera manufacturer. To but it bluntly - they don't work. I had a knock-off for my 30D and used it once or twice and then it just died and refused to take a fresh charge. So, I'd paid $30 for a cheap-ass knock-off battery and then had to pay $40 for a genuine battery. Enough said about cheap-ass batteries!
Aside from modern cameras being power hogs due to the constantly on LCD screen, using AA batteries and switching them out ever 200 shots would rapidly become tiresome - especially when they take up more physical space than the newer LiOn batteries.
I am not a great fan of lithium batteries. Each lithium battery is a potential bomb. They are controlled by electronic circuitry to make sure they don't go critical. Every now and then somebody screws up with their design or the circuitry fails (as circuitry is prone to doing) and there are news reports of devices going up in flames or people being injured by overheating devices. Airlines refuse to transport batteries containing over 2g of lithium because the batteries are so dangerous.
Lithium combined with water produces hydrogen so what we have is a battery that once it catches fire, cannot be extinguished with water. Adding water increases the fire and aeroplanes have very limited fire-fighting facilities hence the ban.
I am a fan of AA batteries. I would like to see the new interchangeable lens compacts taking them rather than the lithium things as they give many more options. Nikon once had a bright idea. They produced a range of cameras powered by the EN-EL1 battery which was lithium but which also took a 2CR5 battery. Those were mighty handy as a backup. They were expensive but there was a viable backup to the lithium battery. Not an ideal solution but a possibility.
In favor of AA batteries is universal availability and many options - lithium, alkaline, rechargeable NiMH etc. Against is the power-hog nature of cameras and the bulkiness of AA batteries. My Canon XT needs 6 AA batteries in the battery grip with a special AA holder. The small Canon lithium holds 7.4v 720mah. 6 AA batteries have 7.2v at 2000mah. In terms of bulk, the small Canon lithium is a lot smaller and lighter. Having said that, taking it from AA to AAA, the bulk is not dissimilar and the capacity of mine is 850mah.
Pentax has had several digital SLRs that run exclusively off AA batteries. Fuji had a few digital SLRs that ran exclusively off AA batteries. It is thus not an impossible feat. If a lithium battery pack was disassembled, inside would be a pair of 3.7v cells. I saw online that somebody had disassembled a Canon NB2LH battery (which powers my XT). There's some circuitry inside but the two individual cells of the $40 battery cost $2.86 each. Mass-produced, the cost of circuitry is negligible as is the plastic case. If we give Canon the benefit of the doubt and said that the component cost was $10 (being very generous) then said that they made $15 markup and the retailer made $15 markup, it's still 150% markup per party as opposed to standard markup of 30% - 40%. Even at 40% markup, the $10 battery would only reach $20 by the time it reached the consumer. Batteries are, as I always suspected, somewhat of a racket.
My conclusion is that not only are we being scammed by camera manufacturers regarding sensor sizes but we are also being scammed by camera manufacturers with the funky batteries. The public is being scammed and systematically milked by the camera mafia.