This may not be new to a lot of you, but I thought I would share in case anyone else is in the same fix. I have an older Planet Bike Alias 10 watt light that hasn't worked in 2 or 3 years because I let the NiMH battery fully discharge. Basically nothing would happen when I plugged it into the charger. The light on the charger would stay red rather than changing to green. I never threw it out because I liked the light and I have a problem with never throwing useless things away.

Anyway, I was experimenting with making a new battery pack with AA batteries, and decided to take another look at the old battery and charger. What I figured out is that the charger doesn't apply voltage/current to the battery unless it can sense the battery is there. If the battery is too dead, nothing happens. So I plugged the battery into one of those "universal" AC adapters that let you select the correct voltage and polarity. After about 10 minutes, the battery had enough juice so that the regular charger would recognize it and charge it.

At first, the battery wouldn't take much charge. The light would run for 15 seconds. However, after several cycles of charging and full discharging, the light ran tonight for 56 minutes (including 51 minutes at full power and 5 minutes in the automatic "limp home" mode). That's about half of what it could do when it was new.

It may continue to get better, but for now I'm thrilled, because that's more than enough time for my evening commute. The light is also way better than what I was using.

Jim S.

I had one of those lights and enjoyed it very much for my commuter.
Bright light good flashing mode.

I sold it a few years back as I upgraded.
Good luck and glad you took the time to work through the problem.

That is called "battery conditioning"

Also (on nicads) sometime VERY briefly hitting them with REVERSE VOLTAGE (in other words, stick them in a circuit with another robust voltage in series and a "0 ohm resistor" will burn through some kind of chemical layer they build up which causes the memory effect. But only do that "shortly" and only do it (check first) with almost dead batteries.

Don't do that with other kinds of rechargeable battery (besides nicads) unless you want to both destroy it and potentially start a fire or worse.

"Conditioning" by full discharge should be done on individual cells, not on an assembled battery. Trying to "condition" an assembled battery will most certainly result in cell reversal, leading to irreparable damage to some of the cells.

The reason the charger refused to recognize the battery is because it must have been one of those "smart" chargers, which attempt to analyze the battery before charging it. In situations like that a simple "dumb" wall-plug charger is often the best approach to perform a slow "reviving" charge of the dead battery.