I got a reply from Cygolite concerning their lights that don't have a automatic charger and using a timer, here is first my letter then their letter:

(My letter)

Subject: charging NiMh batteries

Your Explorer line of lights use a NiMh battery but the charger is not a smart charger so how do we know when the battery is properly charged for the length of time we use the battery?

Isn't the NiMH chemistry is very sensitive to temperature. If I get the battery too hot during charging, as can happen if I buy a cheap wall timer, I will kill the battery.

Don't I need a charger that measures the change in voltage (dV) and measures the change in temperature (dT) to prevent this damage and if so where do we get one and how much are they?

(Cygo's reply)

We suggest following the charging times shown in the manual. A fully charged battery will be warm to touch so you can dtermine if a battery is charged by touching the bottom or sides of the water bottle. If a battery is hot during charging, that means it has reached its capacity and the battery is getting rid of the excess energy through heat.

A timer could help you from overcharging the battery if you do not monitor your charge times.

Sincerely,

Ed
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