Replacement battery for Cygolite HotShot
 

I have a couple Cygolite HotShot tail lights (80 & 150 lumen). The battery failed on the 'Pro' (150 lumen) one. When plugged into USB it just stays on constant rather than the pulsing for normal charging and when unplugged it is totally dead. I swapped batteries with the '80' to verify that the battery is the problem - and I'd rather have the newer 'Pro' be the one that's working.

Wondering if anyone knows a reasonable source for a replacement battery so I could get the '80' working again. It's a Li-ion cell with 830 mA-hr capacity and has a connector at the end of a short 3-wire cord.

Circuit board showing cord and connector:
https://cimg3.ibsrv.net/gimg/bikefor...5273fdffd4.jpg
View of battery from underneath circuit board:
https://cimg9.ibsrv.net/gimg/bikefor...6f477ecc84.jpg

In my experience with lithium batteries, the 3 wires are connections to battery terminals and to protective thermistor. If you find a battery in the right size and have electrical abilities you can generally make it work but if you lack stop here since lithium batteries can burn crazy. Thermistor value will be typically off compared to original, but you can bring it within the range with a resistor in parallel or in series to the original. I have not tried moving the thermistor between batteries, but this is presumably doable. Testing the operation of the thermistor is advisable. Finally, people have also given up on the thermistor, but I do not see a good reason for doing that other than laziness. Again, you are playing with literal fire.

Thanks for the response. I figured I could make something work by modifying a different Li+ cell, but it's not really worth the trouble to me just to rescue a light I could replace for ~$20. Was hoping someone might have a source for a drop-in replacement.

I've searched far and wide for a replacement, but it would appear that, as all of the lights of that form factor use the exact same battery (from the SL to the PRO) that Cygolite had a pack spec'd for them, and they're the only people that have 'em. My HotShot PRO 150 is closing in on it's 2nd birthday and still gets 10-12 hours on triple flash. I was hunting because my wife's HotShot 2W is getting a little long in the tooth, and it seems a shame to retire a perfectly functional light just because the battery is starting to tank. But a PRO is maybe $33, so when the time comes, I'll just pick up another.

Thanks, looks like I'll have to spring for a new light. The battery in the PRO was definitely a premature failure. It was on a bike I keep at my daughter's place in Michigan and had only been used for occasional grocery-getter rides. Was working fine when I left to go home in Calif. but completely dead upon my return half a year later.

Are wires to the battery OK? Maybe it is a simple broken wire issue. You might check whether the battery is warming up when charging. For a broken wire it should stay dead cold.

The battery in one of my hotshots failed in the same way. I sent it to Cygolite. They told me they would charge me $15 to replace the battery. Then I received an entirely new unit instead, at no charge. I can't ask for better than that!

Well, technically, they did replace the battery. :p

Too bad everything doesn't work that way.


-Tim-