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Incredible Color-Changing, Energy-Indicating Batteries!

A practical idea.
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Batteries that gradually fade from bright green (full charge) to red (dead) as the energy within is used up.

Want to see how much juice is left in the remote control? Open up the battery case and take a look!

DrWorm, Jan 12 2010

Integral Battery Testers http://electronics....com/question423.htm
Thermochromics and conductive inks. [csea, Jan 12 2010]

Ultra advanced. http://www.slippery....com/tag/batteries/
How Uber. [2 fries shy of a happy meal, Jan 12 2010]

[link]






       can't wait to hear how it works...
FlyingToaster, Jan 12 2010
  

       Semi-baked for many years on some primary cells (AAA, AA, C, D cells) by Duracell. See [link].   

       One has to press 2 spots [edit, per Jutta] (pressure switches) on the cell to test. This is a good idea to test under a known load, and to prevent current drain under normal circumstances.
csea, Jan 12 2010
  

       Duracell has exactly this. [link]   

       Well, not *exactly* this. Differences between this post and the reality:
- it's a thin strip, not the whole thing
- you have to press two spots to "activate" the tester.
  

       I'd say those test strips are pretty widely known, though. DrWorm, you figure this is close enough?   

       And if not (echoing FlyingToaster's comment), how would you make it work your way? You can't use the existing tester technology, since it consumes (a small amount of) electricity while testing.
jutta, Jan 12 2010
  

       Oop. My bad.
Is there a way that the outer sleeve of a battery could measure its magnetic field strength continuously without drawing power from it?
  

       closest (I think) you could get would be if the casing were transparent and you were using an electrolyte that changed colour as it discharged.
FlyingToaster, Jan 12 2010
  

       //magnetic field strength continuously without drawing power from it?//   

       To gauge the useful remaining energy in a primary cell ("battery") one needs to measure the voltage under load. A battery can produce full voltage open circuit, but be unable to source any current.   

       Also, batteries produce no magnetic field unless they are being discharged (only current flow produces a magnetic field.)
csea, Jan 12 2010
  

       Yes, [jutta], now that I think about it, I may have seen those test strips before... This is essentially a repackaging of the concept, so if anyone wants to, they can mark it for deletion. However, my faith in the wonders of technology is unwavered; I find it hard to believe that this idea is completely impossible.
DrWorm, Jan 12 2010
  

       //I find it hard to believe that this idea is completely impossible// [marked-for-tagline]
pocmloc, Jan 12 2010
  

       My bad...edjukashun Ian. I just assumed that batteries have a magnetic field, not sure why.   

       //not sure why// well they do have + and - poles.
FlyingToaster, Jan 12 2010
  

       Here's a suggestion for how it might work: there are now several types of displays (some MEMS based, and some e-ink displays) that take no power to maintain their state. The battery could be coated with this type of display, and be updated every several minutes if there's discharge, and every 24 hours otherwise by an on-board microchip based monitoring system.   

       Otherwise, if the economics work out you could build an LCD power meter onto a panel on the battery.
cowtamer, Jan 12 2010
  

       [FT]'s anno has me thinking... I know a lead / acid cell's electrolyte changes in specific gravity in relation to charge condition; does anyone know if the pH value changes as well? If so, the color-changing electrolyte might be as simple as adding an indicator to it.
lurch, Jan 13 2010
  

       I would imagine it does change by a little. Not certain it would be enough to be terribly sensitive to.
RayfordSteele, Jan 13 2010
  

       Lessee. Some litmus paper, a 9-volt cell, apply to tongue. Short shopping list to figure pH change, so maybe later.
reensure, Jan 16 2010
  

       Seems like a pH indicator in the electrolyte would work but the range of change is so small that I'm not sure that there is an indicator sensitive enough. If the pH changed dramatically with discharge it would mean that there was inadequate ionic concentration to fully charge and discharge the plates. I'm guessing that a system that measured change in volume would be more effective.
WcW, Jan 16 2010
  
      
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