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So it turns out that I basically have one of these stuck on the negative side of the battery:
battery protection circuit

It's a pair of MOSFETs, along with some reverse-polarity protection.

Looking at the battery for the SD600, a pair of standard CR10440 LiIon batteries would be smaller and last a bit longer (CR10440 is aaa sized).

Three AAA cells takes up a slightly larger area as the SD600 battery (I did a direct comparison on my desk right here) but the AAA battery (three cells) is also nearly twice as thick. A three-cell battery using the CR10440 in parallel (since the two batteries have almost the same voltage) would have 1500 mAh (500 mAh each in parallel) vs. the 760 mAh of the SD600 battery.

The trade-off is camera size. On either side of the battery is the SD card and the display controls, so there wouldn't be any room for the AAA cells unless the camera was made thicker.

So you are correct in that a battery made of AAA Li-ion cells would last longer (nearly twice as long in fact) and be slightly cheaper ($27 for the Canon battery on sale at Amazon.com) but the battery would also take up nearly twice the volume.

You point is well-taken, but my point still stands--it was a trade-off in size vs. battery interchangeability. Depending on what features you wanted in a camera, you can go with one with a proprietary battery or one with standard battery.

As far as interchangeabiliy goes...

If that was a common thing, you could easily get replacement batteries for your laptop at the drug or grocery store. You could interchange batteries between your still camera, video camera, laptop, flashlight, etc. etc. A charger that works on all of them would be $10-$15.

I'll use my MacBook Pro as an example, as I have the battery information readily available. Battery voltage is about 12.5V right now, fully charged, 10.76V when the battery is nearly empty. Battery capacity is about 5500 mAh fully charged. Fully charged, that means in contains about 247.5kJ of energy.

A single AA-size 3.6V nominal Li-ion cell with 900 mAh capacity contains about 11.7kJ of energy. To provide the same amount of energy, you would need over 21 CR14500-series cells. Your number also must be divisible by three, as three cells in series provides 10.8V-the minimum I've seen on my MBP. So you need 24 cells total. Eyeballing the AA cells I have here and comparing to my MBP, the battery volume is roughly the same, not taking into account the interconnections and moldings required to hold 24 cells in an 3x8 battery pack.

So you have 8 groups, three cells per group, to match the 13" MBP battery. 24 cells, at $4.50 sale price from the link given above (bulk price for 24 cells), is $108. The normal price of $7.95 means the cells come to $190.80, slightly less for bulk pricing. You also need to charge all 24 cells at once; you can't mix cells of differing charges, otherwise some cells will have to supply more current than others and potentially exceed their current rating. BTW, I neglected current rating in the discussion as I don't know what the current rating is for a Li-ion cell. It would have to be at least 300mA, as I've seen a peak of 2.4A on my battery and dividing that current over the 8 groups yields 300mA from each. I'm going to assume that each cell can handle 300mA.

Weight: I've seen similar cells at 21g each, but they also had lower (800mAh) capacities. Using 21g anyway, that is 0.047 pounds (rounding up a wee bit from 0.0462 for the extra capacity) per cell, or 1.13 pounds for the battery pack; again, that does not include the interconnecting wiring or holders. I don't know what the MBP battery weights, and I'm not pulling mine apart to check.

So to compare:

13" MBP battery: 247.5 kJ of energy, rated for 1000 charge cycles, and $129 for Apple to replace if it goes bad. Not user-replaceable. Internal connections all soldered together for reliability.

CR14500 battery pack: 280.8 kJ of energy (13% increase), rated at 600-800 charge cycles (20% fewer), similar

Looking at the battery for the SD600, a pair of standard CR10440 LiIon batteries would be smaller and last a bit longer (CR10440 is aaa sized).

Three AAA cells takes up a slightly larger area as the SD600 battery (I did a direct comparison on my desk right here) but the AAA battery (three cells) is also nearly twice as thick. A three-cell battery using the CR10440 in parallel (since the two batteries have almost the same voltage) would have 1500 mAh (500 mAh each in parallel) vs. the 760 mAh of the SD600 battery.

The trade-off is camera size. On either side of the battery is the SD card and the display controls, so there wouldn't be any room for the AAA cells unless the camera was made thicker.

So you are correct in that a battery made of AAA Li-ion cells would last longer (nearly twice as long in fact) and be slightly cheaper ($27 for the Canon battery on sale at Amazon.com) but the battery would also take up nearly twice the volume.

You point is well-taken, but my point still stands--it was a trade-off in size vs. battery interchangeability. Depending on what features you wanted in a camera, you can go with one with a proprietary battery or one with standard battery.

As far as interchangeabiliy goes...

If that was a common thing, you could easily get replacement batteries for your laptop at the drug or grocery store. You could interchange batteries between your still camera, video camera, laptop, flashlight, etc. etc. A charger that works on all of them would be $10-$15.

I'll use my MacBook Pro as an example, as I have the battery information readily available. Battery voltage is about 12.5V right now, fully charged, 10.76V when the battery is nearly empty. Battery capacity is about 5500 mAh fully charged. Fully charged, that means in contains about 247.5kJ of energy.

A single AA-size 3.6V nominal Li-ion cell with 900 mAh capacity contains about 11.7kJ of energy. To provide the same amount of energy, you would need over 21 CR14500-series cells. Your number also must be divisible by three, as three cells in series provides 10.8V-the minimum I've seen on my MBP. So you need 24 cells total. Eyeballing the AA cells I have here and comparing to my MBP, the battery volume is roughly the same, not taking into account the interconnections and moldings required to hold 24 cells in an 3x8 battery pack.

So you have 8 groups, three cells per group, to match the 13" MBP battery. 24 cells, at $4.50 sale price from the link given above (bulk price for 24 cells), is $108. The normal price of $7.95 means the cells come to $190.80, slightly less for bulk pricing. You also need to charge all 24 cells at once; you can't mix cells of differing charges, otherwise some cells will have to supply more current than others and potentially exceed their current rating. BTW, I neglected current rating in the discussion as I don't know what the current rating is for a Li-ion cell. It would have to be at least 300mA, as I've seen a peak of 2.4A on my battery and dividing that current over the 8 groups yields 300mA from each. I'm going to assume that each cell can handle 300mA.

Weight: I've seen similar cells at 21g each, but they also had lower (800mAh) capacities. Using 21g anyway, that is 0.047 pounds (rounding up a wee bit from 0.0462 for the extra capacity) per cell, or 1.13 pounds for the battery pack; again, that does not include the interconnecting wiring or holders. I don't know what the MBP battery weights, and I'm not pulling mine apart to check.

So to compare:

13" MBP battery: 247.5 kJ of energy, rated for 1000 charge cycles, and $129 for Apple to replace if it goes bad. Not user-replaceable. Internal connections all soldered together for reliability.

CR14500 battery pack: 280.8 kJ of energy (13% increase), rated at 600-800 charge cycles (20% fewer), similar

http://www.batteryjunction.com/solar-s-2600p.html

There are also adapter kits and a number of company's that sell the same thing, it's a no name out of china that will charge anything with USB power.

At least those undesirable chemicals are pretty much 100% recyclable. For energy storage like this, you need two things. It needs to be cheap per kwh, keeping in mind maintenance and longevity. Efficiency is also huge - a few points of efficiency can make all the difference, cost wise. Still, a lesser factor than cost, especially when you're simply looking at recovering power that would otherwise not be used.

NiMH is around 66% efficient charge wise, LiIon, though twice as expensive(at this time), is 99.9% efficient.

The extra efficiency would make a huge difference - not so much in the cost of the batteries, but in how many turbines you need to build.

Looks like LiIon is in the same magnitude at durability, ~1200 cycles vs ~1000, assuming excellent battery management, which the power companies would presumably do.

Hmm... Cheap 18650 LiIOn battery 2.4Ah, 3.7V, 8.88 Wh, $5. $.56 per Wh (not suitable for usage in nonsmart charging systems)
Protected 18650 batteries 2.6Ah, 3.7V, 9.62 Wh, $6.69 ea/500+. $.70/Wh

Gotten a LOT cheaper.

Still, Industrial NiMH, 2.1Ah, 1.2V, 2.52Wh, $1.45/500+. $.57/Wh

No wonder so many devices have switched to LiIon!

Still, you're looking at $560-700 for a battery pack to store/distribute $.10 of electricity. Assuming full charge and discharge daily, that's $36.50 of electricity using today's retail prices in my area, but a THIRD of the battery's lifespan. $110 of electricity for the pack's life.

Sigh... Back to the problem with electric vehicles. We 'only' need lithium ion batteries to be around an order of magnitude cheaper to be economical.

At least those undesirable chemicals are pretty much 100% recyclable. For energy storage like this, you need two things. It needs to be cheap per kwh, keeping in mind maintenance and longevity. Efficiency is also huge - a few points of efficiency can make all the difference, cost wise. Still, a lesser factor than cost, especially when you're simply looking at recovering power that would otherwise not be used.

NiMH is around 66% efficient charge wise, LiIon, though twice as expensive(at this time), is 99.9% efficient.

The extra efficiency would make a huge difference - not so much in the cost of the batteries, but in how many turbines you need to build.

Looks like LiIon is in the same magnitude at durability, ~1200 cycles vs ~1000, assuming excellent battery management, which the power companies would presumably do.

Hmm... Cheap 18650 LiIOn battery 2.4Ah, 3.7V, 8.88 Wh, $5. $.56 per Wh (not suitable for usage in nonsmart charging systems)
Protected 18650 batteries 2.6Ah, 3.7V, 9.62 Wh, $6.69 ea/500+. $.70/Wh

Gotten a LOT cheaper.

Still, Industrial NiMH, 2.1Ah, 1.2V, 2.52Wh, $1.45/500+. $.57/Wh

No wonder so many devices have switched to LiIon!

Still, you're looking at $560-700 for a battery pack to store/distribute $.10 of electricity. Assuming full charge and discharge daily, that's $36.50 of electricity using today's retail prices in my area, but a THIRD of the battery's lifespan. $110 of electricity for the pack's life.

Sigh... Back to the problem with electric vehicles. We 'only' need lithium ion batteries to be around an order of magnitude cheaper to be economical.

At least those undesirable chemicals are pretty much 100% recyclable. For energy storage like this, you need two things. It needs to be cheap per kwh, keeping in mind maintenance and longevity. Efficiency is also huge - a few points of efficiency can make all the difference, cost wise. Still, a lesser factor than cost, especially when you're simply looking at recovering power that would otherwise not be used.

NiMH is around 66% efficient charge wise, LiIon, though twice as expensive(at this time), is 99.9% efficient.

The extra efficiency would make a huge difference - not so much in the cost of the batteries, but in how many turbines you need to build.

Looks like LiIon is in the same magnitude at durability, ~1200 cycles vs ~1000, assuming excellent battery management, which the power companies would presumably do.

Hmm... Cheap 18650 LiIOn battery 2.4Ah, 3.7V, 8.88 Wh, $5. $.56 per Wh (not suitable for usage in nonsmart charging systems)
Protected 18650 batteries 2.6Ah, 3.7V, 9.62 Wh, $6.69 ea/500+. $.70/Wh

Gotten a LOT cheaper.

Still, Industrial NiMH, 2.1Ah, 1.2V, 2.52Wh, $1.45/500+. $.57/Wh

No wonder so many devices have switched to LiIon!

Still, you're looking at $560-700 for a battery pack to store/distribute $.10 of electricity. Assuming full charge and discharge daily, that's $36.50 of electricity using today's retail prices in my area, but a THIRD of the battery's lifespan. $110 of electricity for the pack's life.

Sigh... Back to the problem with electric vehicles. We 'only' need lithium ion batteries to be around an order of magnitude cheaper to be economical.

I found a cheaper solution to charging my iPhone by solar. I use two solar arrays, very similar to those found here for $23 each: http://www.batteryjunction.com/12vsopabachs.html They deliver 150 mA max, but I've found they can easily deliver 175 mA each, and not even when angled directly at the sun. I use this with a simple car power inverter that has a USB charger port on it, but you can always make your own 12V to 5V regulator with a 5V regulator from Radio Shack, see here: http://www.radioshack.com/product/index.jsp?productId=2062599 I've used this with my iPhone a couple times and found that it is able to charge my iPhone. There is one trick though, the iPhone is picky about its power supply, and so you need to trick it by making a simple circuit with two resistors. See the post below for instructions (you need to scroll down a bit in the post to get to what I'm talking about, it involves making a voltage divider on the data channels): http://forums.macrumors.com/showthread.php?p=5447947&posted=1#post5447947 Also, it charges the iPhone even while playing music. The first time I tested these was in my car, and I had the panels directed in the windshield. After driving for 3 hours it charged my iPhone from about 60% to 90%; and this was with the panels not angled towards the sun. I haven't taken account of how it charges since, but know it does. Also, if ever the power goes out for several days, you can always pull the battery out of your car when needed (or buy another car battery specifically for this use), and use the power inverter (if it has a USB port) or the 5V regulator to charge your USB electronics. You can then keep the car battery charged with these solar cells, so you don't need to waste gas running the car to charge the battery back up.

Mag may not sell a conversion for your mini but they do exist. These guys make an awesome product that you can buy at http://batteryjunction.com/.