Energy Harvesting of Used Batteries

[Terabyte2007]

I use dozens of batteries a month and most of the gear using these batteries gets replaced when the battery "Low Voltage" sense gets triggered. Needless to say, I have a lot of batteries with charges from .8V to 1.2V. Experimenting with super caps and various other components, I was able to harvest the remaining energy and then dump that into a Lion polymer battery bank and use this collected energy to power other devices and experiments. My next experiment is to measure the energy transfer in mW & mAh to get an understanding of how much energy is harvested from these old batteries (Say, like 25-50 of them). I have found that with a bit of tweaking, I can get quite a bit of energy from these old batteries.

My question, is there a product on the market that already does something similar to this that anyone knows of?

[IanB]

I use dozens of batteries a month...

I guess the obvious question is why not rechargeables?

[Terabyte2007]

I use dozens of batteries a month...

I guess the obvious question is why not rechargeables?

Because rechargeables don't provide the runtime needed, energy density, maintenance, shelf life, costs, etc. It's great for a couple instruments but does not seem practical for dozens of units. I had gone down that road with many failures and elevated costs. Most of the rechargeable batteries on the market are just not delivering the need. And the equipment being powered requires a battery chemistry that Lion or Lipo will not work for. It's more of a pet project to see what I can get out of these used batteries with a relative low cost.

[wagon]

Why not!  If the 'flat' cells are going to be landfill, and not recycled, why not get every last bit of useful energy out of them.  Maybe something that needs 6V (4 cells) gets 5 cells with 1.2V in them.... then 6 cells with 1 volt left, etc.  How much does the current drop as the terminal voltage drops?

[IanB]

Because rechargeables don't provide the runtime needed, energy density, maintenance, shelf life, costs, etc. It's great for a couple instruments but does not seem practical for dozens of units. I had gone down that road with many failures and elevated costs. Most of the rechargeable batteries on the market are just not delivering the need.

OK, I know it's a different question from your original topic, but I would be interested to learn more. I have more or less reduced my purchase of disposable batteries to zero. The only ones I buy are the small 9 V ones and some occasional D cells, and I only buy these because I consume just one or two a year at most. I cannot imagine buying dozens of disposable batteries a month.

[SirNick]

Similar story here.  I'll use rechargeables anywhere I can -- cordless mice, some remotes, etc.  Certain devices just don't work well though.  Examples:

- Wii-motes.  I don't play often enough, so they're guaranteed to be Dee-Eee-Dee, dead, by the time I use them.  If it's a party game, that's four Wii-motes with two AAs each, so eight AAs that need to be charged and ready at any given time.  I'm lucky to have two charged AAs available.

- Cheap spinning toothbrush.  The power draw profile isn't particularly friendly for NiMH cells.  A pair of alkies will last a while anyway.  Maybe some day I'll buy one of the nice ones with internal batteries.

- One older digital camera I have will shut off after like a dozen pictures.  Not enough current capacity and/or it's too aggressive with the low-battery thresholds.

- Various remotes that don't get used often enough.  The self-discharge of NiMH cells means that they are basically only there to show the proper orientation of the alkaline cells that need to be inserted now if you want to use this thing.

- Wireless audio stuff.  I have an in-ear monitoring system and a guitar pack transmitter that I've tried using rechageables for.  The in-ears use a pair of AAs, and they work OK, but the battery meter is off by enough to mean you're really just guessing whether you have enough power to get through a set.  NiMH 9v cells are a complete and utter waste of time.  They will die before the lead guitarist has finished the intro to Stairway to Heaven.

[NiHaoMike]

Have you tried low self discharge NiMH?

[SirNick]

Not I.  I'm going off the batteries I can find on the shelf at local retail.  That would resolve some issues (forgot to add: wall clocks).  Voltage per cell and internal resistance are still issues though.

Not my thread though, so I'm going to quit bogarting. 

[IanB]

Have you tried low self discharge NiMH?

Not I.

Oh boy. Then you are really not getting the benefit of rechargeable batteries. You can charge up AA Eneloops and they will still work fine two or three years later. Self-discharge is so low that alkaline batteries will leak before Eneloops run out of charge.

- Wii-motes.  I don't play often enough, so they're guaranteed to be Dee-Eee-Dee, dead, by the time I use them.  If it's a party game, that's four Wii-motes with two AAs each, so eight AAs that need to be charged and ready at any given time.  I'm lucky to have two charged AAs available.

See above. Put Eneloops in them and they will always work when you pick them up.

- Cheap spinning toothbrush.  The power draw profile isn't particularly friendly for NiMH cells.  A pair of alkies will last a while anyway.  Maybe some day I'll buy one of the nice ones with internal batteries.

I use a (not super cheap) Philips Sonicare that takes two AA cells. A pair of Eneloops last about a month between charges.

- Wireless audio stuff.  I have an in-ear monitoring system and a guitar pack transmitter that I've tried using rechageables for.  The in-ears use a pair of AAs, and they work OK, but the battery meter is off by enough to mean you're really just guessing whether you have enough power to get through a set.  NiMH 9v cells are a complete and utter waste of time.  They will die before the lead guitarist has finished the intro to Stairway to Heaven.

Yes, NiMH 9 V are hopeless, but lithium ion 9 V cells work great for wireless mikes and other wireless audio gear.

[wagon]

Most 9V rechargeables are only 7.2V.  You used to be able to get true 9V rechargeables (must have been 8 cell).

[IanB]

Most 9V rechargeables are only 7.2V.  You used to be able to get true 9V rechargeables (must have been 8 cell).

It's not the voltage that's the problem, but the need to put several cells in series. That and the limited capacity of the small battery.

[Rufus]

My question, is there a product on the market that already does something similar to this that anyone knows of?

No because it is stupid.

The energy in a brand new 'D' (or MN1300) battery is about 7 Wh. At US mains electricity prices that much energy from the mains would cost between 0.07 and 0.14 cents.

100 flat D cells, the harvesting contraption and your time to plug them in and out would earn you 1 cent worth of electricity.

[miguelvp]

Not D batteries but AA or AAA for $0.15 per cell (because there are single so they are not batteries )

http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=7490098

[G7PSK]

I tend to only use AA batteries in clocks these days and have found that after a year they are around 1 volt or less and very often they will run in a clock for 18 months if left but I normally change them all when setting to daylight saving time. I see no point in using rechargeable for such duty and there so little left in them that trying to get the extra would not be worth the time.

[Terabyte2007]

How much does the current drop as the terminal voltage drops?

If I have time, I will mock up a test with my DC Load, much like I do for energy extraction, and capture a curve. It's fairly linear until about .4V and then drops pretty quick. That also depends on the battery maker too. I found if I can regulate the current flow even if it's small it still works good. I am going to try and simplify my process and design an interface board that does the energy extraction. I have always been bothered by the waste of this energy from batteries that still have quite a bit of energy left in them, although not useful for their intended equipment voltage rating, still perfectly capable of  delivering energy. Take for example a 9V battery, most equipment indicate low battery status at around 7V, some lower, some higher but the energy left in a 9V battery is quite significant.

[Terabyte2007]

Most 9V rechargeables are only 7.2V.  You used to be able to get true 9V rechargeables (must have been 8 cell).

I have Tenergy Lion 9V and they are all around 8.4V fully charged. Not too bad.

[Terabyte2007]

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.

[wagon]

Most 9V rechargeables are only 7.2V.  You used to be able to get true 9V rechargeables (must have been 8 cell).

I have Tenergy Lion 9V and they are all around 8.4V fully charged. Not too bad.

Pretty good.  Those weren't available until fairly recently.  I think the 9V type were made by Varta or something.

[Terabyte2007]

My question, is there a product on the market that already does something similar to this that anyone knows of?

No because it is stupid.

The energy in a brand new 'D' (or MN1300) battery is about 7 Wh. At US mains electricity prices that much energy from the mains would cost between 0.07 and 0.14 cents.

100 flat D cells, the harvesting contraption and your time to plug them in and out would earn you 1 cent worth of electricity.

It's not about making money or selling a product. It's about waste. Call it what you will, as you say "Stupid". I don't think so. It does not take much time out of my life to do this nor much expense. I don't feel getting every last mW of energy possible from a battery is stupid, what's stupid is to toss half used batteries into a landfill (Which should not be done in the first place) instead of re-purposing them in other ways for their second half of life.

[saturation]

I've had a similar dilemma for decades in a work environment, we use a lot of 9V and AA cells to power wireless monitors, and do not use rechargeable for the same reason as the OP.

I can see a value in this for an organization using hoards of batteries but the reclamation of energy versus the human labor to keep doing this could be inefficient, so you'd have to weigh the cost/benefit.  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.

Instead of harvesting the remaining energy in used batteries, we collect old cells in a box and reuse them as is, any employee can take them home.

Since the device low power indicator is fairly constant, the remaining power in the batteries are fairly fixed so after a few are sacrificed to determine remaining Wh or Ah its expected adjusted lifespan can be estimated for the type of cell within the whole bin.

Used 9V work well multimeters and some alarm applications [ gives 1 year instead of 4], AA are more versatile, it lasts ~ > year running wall clocks, remote controls, and LED pocket lights with constant current circuitry.  With the increasing deployment of wireless keyboards and mice in new desktops in lieu of wired items, most use AA, these batteries are perfect in them as they last also for ~< 1 year versus the new battery life of => 2 years.

[Rufus]

It's not about making money or selling a product. It's about waste. Call it what you will, as you say "Stupid". I don't think so. It does not take much time out of my life to do this nor much expense. I don't feel getting every last mW of energy possible from a battery is stupid, what's stupid is to toss half used batteries into a landfill (Which should not be done in the first place) instead of re-purposing them in other ways for their second half of life.

Tossing half used batteries into landfill is a waste. Extracting the energy from them to charge some other battery before tossing them into landfill is a bigger waste. It is the kind of technically illiterate, arithmetically challenged eco green tosser gesturing that makes me want to puke.

Adjusting your heating or A/C thermostat by 0.1 degree will save or use more energy than you will ever recover from your used batteries.

[G7PSK]

It's not about making money or selling a product. It's about waste. Call it what you will, as you say "Stupid". I don't think so. It does not take much time out of my life to do this nor much expense. I don't feel getting every last mW of energy possible from a battery is stupid, what's stupid is to toss half used batteries into a landfill (Which should not be done in the first place) instead of re-purposing them in other ways for their second half of life.

Tossing half used batteries into landfill is a waste. Extracting the energy from them to charge some other battery before tossing them into landfill is a bigger waste. It is the kind of technically illiterate, arithmetically challenged eco green tosser gesturing that makes me want to puke.

Adjusting your heating or A/C thermostat by 0.1 degree will save or use more energy than you will ever recover from your used batteries.

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

[IanB]

I have not tried the low discharge yet, mainly because I have given up on NiMH cells pretty much.

"I don't use the good design that works well, mainly because I have given up on the unsatisfactory design that doesn't work well."

I have trouble following the logic.

[Rufus]

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.

[timb]

I've had great luck with MaximalPower brand rechargeable 9V Lithium Ion batteries. You can get them on eBay or Amazon.

In my tests the starting voltage is about 9.6V and I got a consistent 560mAh out of two units I tested, over 5 charge/discharge cycles each.

The total runtime was similar to a Duracell brand Alkaline.

So if you want to throw money down the drain, be my guest. Otherwise, the technology is out there now.


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