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I have an older CygoLite headlight that I used for commuting for a couple years. It's been in storage for about 12 months, and now it seems like the battery won't take a charge. I think its a variation of a NiCad battery, not lithium. The battery looks like this:

CygoLight Gel Battery

Is there a way to recondition a battery or do I just need to replace it?

Note - I have plugged the light assembly into another similar battery and it works, so I know it's not the bulbs.

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With a NiCad light that only held a few minutes charge I've had decent success with a full drain/charge or two to get life back. Never done that with a totally dead one, though. –  freiheit Sep 12 '11 at 14:40
    
It might be a acid gel cell, does it specifically say what it is? –  Moab Sep 12 '11 at 15:50
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Wy limited understanding of batteries is whispering in my ear that whether this can be done will depend heavily on exactly what sort of battery this is. This is on-topic for this site, but I'm guessing you might get a more complete response over on the Electrical Enineering site. –  Neil Fein Sep 12 '11 at 19:11
    
Well, you've got an electrical engineer right here. Could well be a lead/acid gel cell -- more likely than NiCad. If it's a gel cell it very likely is a standard size that can be replaced without real serious disassembly, though it may involve some soldering. The gel cell will be a single "brick" (or maybe two), generally of black plastic. NiCads will be cylinders that look more or less like regular flashlight batteries, with metal strips spot-welded on the ends jumping from one cell to the next. The lead/acid battery is heavy, but had several times the capacity of NiCad for the volume. –  Daniel R Hicks Sep 12 '11 at 22:35
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The battery is probably shot but the battery pack can be rebuilt. An outfit like "Batteries Plus" (in the US) can do it. Or you can generally do it yourself if you're fairly clever (though getting it professionally rebuilt is better because they have the right spot welder, etc).

(It would be nice if the light mfgrs would use standard tool batteries rather than their own designs. It would be fairly easy to build an adapter to hold one in a water bottle cage, eg, and then replacements would be readily available and you could use the tool charger.)

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As for spot welding, you can have some success with a solder iron although the specific heat capacity of a battery is high so you need a big solder iron to get some solder to actually stick. –  ʍǝɥʇɐɯ Sep 12 '11 at 16:18
    
Yep, and if you overheat the battery you damage it. And the plating on the battery terminals is often resistant to solder. –  Daniel R Hicks Sep 12 '11 at 22:36
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