After 5 years, the NiMH battery stopped holding a charge for anywhere near as long as when new. I mostly used it in Flash mode, but the red Low Battery light stayed on all the time. Cateye isn't selling the batteries anymore for this model, and I searched without success until what seemed like the end of the Internet.
Ventured into a local Batteries Plus, just on the off chance they had something in stock. No, but they said they could rebuild the pack. Really, how much?
Well, OK then, let's do it. When I went back to pick it up, the manager said the guy working had quoted me too low of a price, but he would honor the deal. The mAh of the new batteries was more than double the old batteries.
When I tried to put it together, I realized just how tight the tolerances were. Had to de-solder the wire leads, solder some additional wire onto the red lead, trim off some of the black lead, and use my Sears knockoff Dremel tool to trim off part of the "battery tray". It's a snug fit, but I got it back together without pinching the wires or the gasket too badly.
The red Low Battery light was still on, even after charging. I started to wonder if I'd wasted $20 and would have to end up replacing the light anyway.
I ran a "stress test" this morning, and the light lasted close to two hours on High. That's the manufacturer's approximate operating time on High. Recharging it now.
Even though the mAh rating of the batteries is higher, I'm wondering if the factory charger will be able to fully charge them. It's been years since I sat in an electronics class.
One really puzzling piece is a component in the battery pack soldered between the middle two cells. I've done some reading, and I get varying information. I thought it was a thermistor at first, but now I'm not so sure. The markings include Ucera UK-32 105C (which I believe is 105°Celcius). I found it here, and it's identified as a thermal protector.
I'm still puzzled way anyone would want to throw money at fixing something so old. With that said I've own a couple of the ( then ) small Cateye Halogen lamps. Even when they were new they were really only good for "blinkie" see me duties.
You got very lucky. A custom battery rebuild usually does cost more than $20. The guy that gave you that quote probably got a-talking to.
Moving forward, the new mini USB lights are so much better ( smaller size and larger output ) that using something like one of those old Cateyes makes no sense ( "unless you like having your handlebars cluttered with clunky out-dated stuff" ).
Cateye Nano is, for practical purposes, the same size. It's also about $80. If this lasts 3 years, I suspect the price of NiMH batteries will be such that I could solder up a replacement pack myself for under $10.