Step 1: Verify What the Problem Is
This Instructable 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 Instructable might be for you!
Step 2: Find a Donor Power Supply
Since my 15v power supply is pumping out 3v, I need something else that has similar power ratings.
The new supply
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.
Step 3: Swap Power Supplies
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.
Step 4: Make the Wiring More Permanent
I soldered the wires to the original connection points and even made a pull-stop so pulling the cord wouldn't yank the wires out of the circuit board.
Step 5: Reassemble
Simple, put the thing back together
Step 6: Results
Oops, it looks like I need to test my batteries with the multimeter every time I charge for more than 5 minutes now, because the new charger is a bit overpowered... Once again finding a more closely matched power supply would have helped.
Step 7: Final Test
There you go, the light comes on and charging commences. It looks like this project is complete.
Again, I put more details on my blog post , but the steps are the same.