Use a garden lamp to charge batteries. This lamp cost $4.00. I used it to charge the batteries for my beard trimmer.
Take out the three screws holding the unit together.
Insert the battery you wish to charge. Mine was an AAA, so I had to strech the spring and pop the positive connector out and reposition it.
Then just put it back together and place it in the sun for a day or two. You'll have to take the battery out before it gets dark or it will light up and use power. I suppose you could cut the wires to the diode if all you need it for is charging.