This lets fix it assumes that you identify that the problem is the charger itself. In my case, a 15v power supply to charge 12v batteries was pumping out 3v. Get a simple multimeter and measure the voltage at the terminals of the charger. If the voltage is less than the rated voltage, then this lets fix it might be for you!
Since my 15v power supply is pumping out 3v, I need something else that has similar power ratings. The original: 15v, 200mA The new supply 15v, 800mA Well, the replacement is a bit overpowered, so there is a little danger here. If possible, find one that is a closer match than this one.
I cut the wires to the original power supply, and tested the performance of using the new power supply before making it more permanent. It worked as it should - actually, much faster than it should. I need to be careful not to overcharge.
There you go, the light comes on and charging commences. It looks like this project is complete.