I saw some non-rechargeable batteries in the house. They were for a label printer that isn't used much and gets through one set of batteries in about five years. So it's not worth getting rechargeables. Or at least it seems intuitively like it's not worth it. At least it may not be worth it financially.
In terms of environmental impact, it's probably always worth getting rechargeable batteries. Even if they are just going to sit in a device for ten years. At the end of the time, they can be taken out, recharged and reused somewhere else.
I'm not really sure why they have to be so much more expensive than one-use dry cells. I'm sure a lot of the costs are the same. In fact I found with CR2s that I could get rechargeables online cheaper than the non-rechargeables in the local electric shop.
A battery has a metal case, which makes the anode. It has a rod down the middle, making the cathode. Between them is some chemical compound which can store and release current. The chemical compound is different, but it's only a few grammes. It's not like it's gold.
The costs are all wrapped up in economies of scale, and dry cell batteries are cheaper because more of them have been made for longer. Edison-style incandescent light bulbs aren't cheaper than LEDs because there are fewer resources, or because it's intrinsically easier to make vacuum-filled glass bulbs but because factories have been set up to make them, and the plant is all paid for. In fact once the plant is in place, LEDs are likely to be cheaper.
Also, the rechargeable batteries are more expensive because of supply and demand, since people are prepared to pay for more, and because the extra cost and the sale of battery chargers can mean more shop shelf space.
What would really make sense is solar-powered batteries. When they go flat, you could leave them somewhere in sunlight, like a windowsill. The tricky part would be to get the charging circuit to work with the battery characteristics to ensure effective charging without any memory effects, and without shortening the battery life. They may take a few days to charge, but batteries come in a few standard sizes, and you can get extras.
The solar panels would also need to be tough, since they represent the outer casing, so a next generation of solar cells is needed.
There, I've written about it, now I'm sure if I search the web for a few minutes I'll find somebody has made some.
