I pick on the AA size because most of the battery-operated toys, gear, equipment, knickknacks, what have you are operated on this size, but let's open it up to the other popular sizes, too, the C, D, AAA and the pointy-eared rectangular 9v (an actual "battery" as it contains 6 cells).
In my house, I have a few batteries in use:
Bedroom: clock-radio (9v for time backup), a flashlight (3 D), a reading lamp (2 AA) and a weather alert radio (takes 3 AA, but not in use)
Dressing room: Clock (AA)
Upstairs hall: Smoke detector (9v)
Downstairs hall: Smoke detector (9v)
Bathroom: Clock (AA)
Living room: Clock (AA), stereo remote (2 AA), VCR remote (2 AA), TV remote (2 AA), Caller ID box (9v, data backup)
Various Items of clothing: Flashlight (2 AA), Laser pointer (2 AAA), another flashlight (2 AA), Palm Pilot (2 AAA)
Various bits of geeky gear not listed above: GPS (2 AA), another flashlight (AA), a fluorescent reading light (4 AA), a shortwave radio (2 AA + 6 D), TRS 80 Model 100 (4 AA), RS-232 breakout box (2 9v), handheld radio scanner (4 AA), frequency counter (AA), antenna analyzer (10 AA), HP calculator (3 N -- an N cell is like a half-height AAA cell)
Other stuff: There's a boom box somewhere that I just put 6 D into.
Absent from this list is a whole boxcarful of amateur radio gear that uses customized rechargable batteries (Oh, there's a morse code keyer that uses 3 AA). I haven't even stepped down into the basement to see what I might have down there. Nothing I'm actively using, to be sure.
Let us summarize: D: 15, AA: 45, AAA: 4, 9v: 6, N: 3; total: 73. Note, that this is a casual survey...I know for a fact that there are other surprises awaiting us.
Many of these last a long time. Smoke detector batteries usually go about a year, as do backup batteries. Since we use AC power when we can, the batteries I put into various radios last quite a while. Probably the hungriest thing I own is my Palm Pilot. If I'm using it as a bookreader, I eat a pair of AAA's every 2 weeks. Otherwise, I can get 6-8 weeks from them. I've gone thru 24 AAA's in the last 6 months.
Anyway. 73 batteries. Make that 75, I just saw two more while sitting here typing. These are manufactured somewhere, used up, and end up in a landfill. (Only about 14 of these are rechargeable AA's) All of these have some sort of chemicals in them which have to be packaged in standard-sized containers. Eveready Battery Comany makes 6 billion cells a year. Ask yourself: What if they stopped? Never mind the potential effects on the environment from their manufacture and disposal.
What if they stopped? What if a war caused rationing, or critically damaged the technology base we need to keep making these cells? What if the governemt stepped in to reduce the supply, perhaps because the EPA found out the manufacturers weren't being good corporate citizens after all. What if the price if a AA cell skyrocketed to $5, $10 or more?
I'm a geek. Stuff like this keeps me awake. But I have my slide rules. I just need to go out and get one of those shortwave receivers with the crank-up flywheel, and a few solar cells.
Pleasant dreams, gadgeteers!