what button cells can you recharge?/ super capacitor help

what button cells can you recharge? For example, some are in calculators wtih solar panels, do they need a complex charging circuit? I'm building a bunch of tiny circuits and I don't want to keep on changing the battery. edit, I now need help with super capacitors

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westfw9 years ago
With a supercap, you're also going to be affected by the rather non-ideal discharge curve; your cap will still contain 1/4 of the original energy when it's at half its original voltage...
You know that Cooper Bussmann, one of the supercap vendors, has a nice spreadsheet for this sort of thing?
At ~5mAh/day power requirements, a typical non-rechargable battery will last quite a long time...
guyfrom7up (author)  westfw9 years ago
I might just go with a watch battery, I mean an average cr 2032 battery (get a bunch from dealextreme, 3.57 for 20, probably 15 cause some will be dead, but that's a great deal. One battery could power my device for about 800 hours, or about 80 nights, which is a terrific deal! This equates to about 0.2 cents a night to keep it on, I'll definately go with a battery, thanks!
zachninme9 years ago
I'd just use a capacitor (designed for this sort of thing).
Now that I think of it, I remember seeing a LED light that you plugged into the USB port to charge -- it was a really simple circuit: a button, an LED, and a resistor or 2)
guyfrom7up (author)  zachninme9 years ago
it was the super capacitor light instructable, right? That's actually a pretty good idea, I'll look into how many farads I need for my aplication. Super capacitors are a bit more expensive than a cell though...
guyfrom7up (author)  guyfrom7up9 years ago
to find out what size cap I need, does anyone know how many farads to a Mah? For example, how many Mah does a 1 farad cap have at 5 volts?
guyfrom7up (author)  guyfrom7up9 years ago
I just calculated it, and I need 2.65 mah, so how many farads is that?
guyfrom7up (author)  guyfrom7up9 years ago
can someone double check me on this, do I need a 7.3611111111111111111 Farads for this
capacitors give almost unlimited amps, but only for a short burst of time. they are fairly unlimited in that respect
Goodhart9 years ago
As for batteries, there are places like this that sell these batteries, but that is only an example, I know nothing about the company.
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