I want to salvage this LED from a rechargeable work lamp if possible to use as a work bench lamp, it had a 7.4v battery but the PCB is dead, can I test the LED straight from a dc power supply ?

If it works what is the correct voltage to run it and what cheap off the shelf regulator pcb is available for my 12 v solar system ?

 

Your first step is to determine how those LEDs are wired.

 

You can try using 12VDC but make sure that you limit the LED current by using a 1k-10kΩ resistor in series with the LED and power supply. Start with 10kΩ and work down until the LED turns on. Try connecting in one direction then in the reverse direction.

Edit: I meant to say, test one LED at a time. You might find some are good and some are bad.

 

An examination of the failed power control PCB may reveal clues as to the supply voltage. OR, there may not be any intermediate control assembly. Without additional information, such as seeing the rest of the system clearly, the best that you will get are random guesses. Based on the one photo, there is some module that we do not see connected between some other portion and the LED module.

What you have is an LED array requiring an unknown voltage at some current to deliver light. So the short answer is "Probably yes, BUT." And the "BUT" is that we need to know a bit more. With NO additional information, the process will be to use a regulated variable voltage power supply, with a series resistor to limit the current, to apply a voltage, starting from about 5 volts, slowly increasing, until the LEDs illuminate adequately. Then measure the applied voltage and that will be the supply voltage needed.