I have a cheap (< $10) handheld spotlight that no longer works. Maybe the problem is as simple as a dead sealed lead acid battery.
Observations:
* The battery's voltage measured 0V initially when I first opened it up after having the device non-functional since a few years.
* After "charging" for several hours, the battery voltage measured ~2V. The light would not turn on.
* The light bulb does turn on (dimly) with a 1.2V AA battery, so the bulb is not dead.
* The bulb seems to be a halogen, stamped "H3 4V15W".
* The charger says output is 6V 300mA, but a DMM measures ~11.5V at its output terminal (with nothing connected) ??
* The voltage at the battery terminals with the charger measures ~10.5V.
* There is a sticker on the outside that reads: "Never turn light on while charging as it will damage unit." This may have happened...
* Another sticker reads: "Do not recommend to charge the unit for more than three hours using the DC cable to avoid battery overheating. Ideally the battery could be fully charged by household adaptor within 12 hours."
So... 3hrs or 12hrs or?? It has previously been left charging overnight. Currently when I try charging, the battery remains cold to the touch.
I'm guessing the battery is simply dead, yes? The rest of the circuit is just a switch, a couple of resistors (1 kilo ohm, 3.3 ohm), a diode, and an LED. What could be the cause of death? What do you make of the warnings?
Secondly, are there suggestions for a modification to allow the light to function both from battery and/or from the charger?