Energy Harvesting of Used Batteries

[NiHaoMike]

There is a considerable amount of energy to be reclaimed in SLA automotive batteries that is useful when the battery itself is too worn for automotive use.

Most car batteries are flooded lead acid, not SLA. Which is actually better for repurposing as flooded lead acid seems to respond better to the "dimmer, motor run cap, and bridge rectifier" desulfating trick.

[G7PSK]

Not supposed to send batteries to landfill here, they get recycled for the chemicals and metal etc.

Alkaline and Zinc chloride batteries are not worth recycling. Since the removal of trace mercury and cadmium years ago they present no environmental hazard. Taking them to a recycling centre (who will put them in landfill) would be another pointless green gesture with actual negative impact on the environment.

The Zinc can easily be reclaimed even after being consumed by the chemicals in the battery and is well worth doing.

[IanB]

The Zinc can easily be reclaimed even after being consumed by the chemicals in the battery and is well worth doing.

However zinc is an abundant and inexpensive metal. The economics of reclaiming it from spent batteries would be an interesting subject.

For comparison, consider that US pennies are made mainly of zinc and there may be something like 500,000 metric tonnes of them out there somewhere. That's a lot of zinc that could be reclaimed from coins that most people toss into a corner and ignore.

[mzzj]

Have you tried low self discharge NiMH?

I have not tried the low discharge yet, mainly because I have given up on NiMH cells pretty much. I have read the Enloop are pretty good, but nothing seems to beat a well made alkaline or even lithium battery.

Eneloops are sooo much better than anything before them that its really apples vs oranges.  Seem to have great self-life too.

There is still a place for alkaline AA's like clocks and other equipment where batteries last like 1-5 years. Even if Eneloops seem to have great self-life I doubt how well they do after 20 charge cycles in 1-5year wall clock (that is 20 to 100 years!)
Price difference is something like 10:1 or 20:1 so if you manage to get 10 to 20 charge cycles for a rechargeable Eneloop its break-even.... (assuming that you don't lose your batteries somewhere during their lifetime) 

I use mostly LSD-nimh's and for picky equipment these: http://www.energizer.com/batteries/performance-lithium/ultimate-lithium/Pages/aa.aspx

[wagon]

I built a remote control for a machine recently and needed a power source.  I thought about going rechargeable, but went with six 1.5V AA lithium cells.  Whilst not cheap, I expect they'll last over a year and all of the hassles with charging and stuff are gone.  (The remote controls a  large mulcher and lives in the not very clean cabin of an excavator)  I expect the lithium cells will be running the remote transmitter down to around 1 volt per cell, which is pretty decent IMO.

[macboy]

While academically interesting, this is a futile effort. Consider that a new AA alkaline cell may have 5000 mAh capacity at nominally 1.5 V; that is 7.5 Wh of energy. Energy costs vary of course, but USD $0.25 per kWh is a good (high) estimate. So each Wh is valued at $0.00025, and the energy in a full AA is worth approximately two tenths of one cent. The residual energy in a depleted cell is, what? maybe one-tenth of the full amount? Then you need to "harvest" the energy from 50 used cells to save one cent.

Is it worth your energy?

[Terabyte2007]

While academically interesting, this is a futile effort. Consider that a new AA alkaline cell may have 5000 mAh capacity at nominally 1.5 V; that is 7.5 Wh of energy. Energy costs vary of course, but USD $0.25 per kWh is a good (high) estimate. So each Wh is valued at $0.00025, and the energy in a full AA is worth approximately two tenths of one cent. The residual energy in a depleted cell is, what? maybe one-tenth of the full amount? Then you need to "harvest" the energy from 50 used cells to save one cent.

Is it worth your energy?

I fully understand this. I never intended on developing and marketing a device. My intentions were much more on the academic/experimental side than anything else. I spend a lot of my free time experimenting with different concepts, materials and unique electronics projects. Some fail while others are successful. I think outside the box and if that is a crime then so be it. I have loads of data from my experiments which have yielded some very interesting results. Some of my experiments are very fringe and I get hammered quite often for these practices. I merge electronics, biological, chemical and materials sciences into my experiments which some, I don't dare speak of because of a lack of acceptance by mainstream thinking. I do however present to a limited live audience locally on occasion some of my more successful projects with some very interesting and positive feedback.

Is it worth marking? Probably not. But what I learn from some of these experimental projects is extremely valuable to me.

[ElektroQuark]

You can look for one of those energy harvesting ICs. Or something like a joule thief.

[SirNick]

The Joule Thief was my first thought, too.  Figured OP had probably been there done that, though.  If not, well there ya go.

BTW, I'm 100% all for doing something for the heck of it.  Not every... scratch that, no aspect of a hobby has to be rational.  For that matter, I always try to find less demanding applications for dead batteries too.  It's not about the equivalent grid cost, since most of these devices can't be run from the grid anyway.

Incidentally, my bathroom wall clock has served as a battery tester four times in the last couple weeks, going on number five... as its time will be correct in about 8 hours, for around one minute.

[Melt-O-Tronic]

I like this idea and have thought about it before.  I have a game camera that takes C batteries only and it gives up when they're only about 60% discharged.  So I have a stack of them with no other uses.  I'd love to drain the remaining energy from them into my collection of Eneloops that I use for everything else.

I have some Joule Thiefs laying around here somewhere.  I need to dig 'em out and see what I can figure out.