Thanks for the tip about low discharge NiMH batteries. That has been one of the main downsides of rechargeables for us.
On the topic of whether products pay for themselves over time and whether it is worth purchasing more efficient and so called "environmentally friendly" products in the first place (since they often initially cost more), I personally don't let that hinder me from purchasing something if I feel it will improve my overall circumstances. There's no doubt that some things take many years to recoup their costs. But why let that stop you from using it? People waste a lot on money on many aspects of their life anyway e.g. food, clothing, personal care, entertainment but few people would do a cost benefit analysis on those.
Sure, there are lots of reasons people do things - but it pays to be clear about what the trade-offs are. If you are getting a device to save money or to reduce electricity use, or be quieter, it is well to be clear to what extent it will actually do that. (Separate marketing fluff from reality.) [If we could just trust the marketing, we wouldn't need SPCR to share experiences on what actually works to make a quiet computer, e.g..]
Actually, lots of people do cost-benefit analyses on things like food. There are plenty of advocates of eating local, eating less meat/more vegetables, etc., places like the Center for Science in the Public Interest which analyze the contents of food and point out the benefits and hazards, and places like Consumer's Reports which compare products to see how long they last, how much upkeep they take, etc. Lots of people on limited budgets, or who are health conscious, shop with care.
For some, "green" is more to do with the economics of the daily aspects of managing a household because of rising living (especially energy) costs rather than caring about every aspect of environmental impact. Whether that's right or not, for a lot of people, that is the case.
Which is when you need the calculator or measurement -- to see if a given investment/device really improves the economics. (Or just gives a "green" appearance to conspicuous consumption.)
After all, to offset the costs of buying a typically fat/sugar/cholestorol filled lunch of a burger, chips/fries and soft drink you will have to jog at least 500KMs before you can break even on the cost of harming your health.
Jogging 500km (310mi) at 5mph, a 160lb person would burn about 36,000 calories. (Based on 584 calories/hour - from Mayo web site). A triple whopper with cheese has a mere 1,230 calories - they must have some amazing burgers/etc. to pack in 30x the calories.
(Of course I suppose 160lb people probably don't eat that kind of lunch.)
Anyone got a calculator? I think mine needs new batteries.
Get a solar powered calculator - doesn't need batteries.