I purchased several of these little solar garden lights from Walmart for 97 cents each. From past experience I know that if you can get these to function for more than a month, consider yourself very lucky. The light output is very weak, and the rechargeable batteries they put in these are the cheapest they could find. They figure if they only charge 97 cents, it's easier to just buy more replacements than it is to complain about it.
For this Instructable, you will need:
Instead of buying more replacements, or complaining, I decided to go a 3rd route and make them function better by replacing two of the components that make them so cheap. I replaced the sad little white LED with a brighter (and yellow) LED to get some decent light output, and I replaced the cheap battery with a better quality rechargeable Ni-Cad so they would last much longer.
Step 1: What's Inside...
The clear plastic lens separates easily from the main black housing by twisting them apart. The housing will come apart into two pieces when you remove the two screws. Inside you will find the cheap battery, in this case a 2/3 AA. The link above is where I found my rechargeable Ni-Cads for about $11 for a pack of 4. The circuit board is (or should be) held in place by a bit of silicone adhesive. Pry this loose with a flat screwdriver and the circuit board should come out easily. Remove any excess bits of adhesive.
Step 2: Removing the LED
Get your fine tip soldering iron and some braided wick to remove the old LED. You can get by without the wick, but using the wick to remove excess solder makes this much easier. Some of these lamps have little sleeves covering the leads. Don't lose these. Not only do they prevent shorting, they also make a nice gauge to control how far the LED leads go into the circuit board.
Step 3: Adding the New LED
Once the old LED is out, insert the new LED (and sleeve on each lead) making sure to put the longer lead into the positive (+) side. If you reverse the polarity/leads, it won't work. Solder the leads in place and clip off any excess from the solder side of the board, then bend the LED 90 degrees so that it will fit into the housing, matching the one you replaced.
Step 4: Putting It Back Together
Slide the circuit board back into place so that the top of the LED goes into the hole in the center, and put a drop of glue or silicone on the board next to the housing to hold it in place. Put the two pieces of the housing together and replace the 2 screws.
This is my first instructable, and I hope you found it useful!