Solar battery chargers make good economic and environment sense. It just gets better when you realize that you don't have to use any mains electricity at all to recharge your batteries when you can simply use the power of the sun.
Things You Need:
1) AA Battery Holder
2) 9 V Battery Clip (This is to establish connection to your battery holder)
3) 8 x Solar Cells 0.5V, 20 to 50 mA in full sun
4) IN5818 Schottky Diode
This is a very simple circuit which doesn't provide any regulations. All you need to do is to disconnect your batteries when they are recharged.
The Schottky diode prevents the batteries' charge from flowing back through the solar cells when no charge is present. Schottky diodes have the advantage of not sapping too much of the power from our solar cells, maximizing the amount that is delivered to the batteries.
If you happen to live in a climate where the sun is a rare treat and it is often overcast, you might like to experiment with a couple of additional cells in series to increase the power produced.
The construction process isn't difficult at all. There are wide arrays of cases available that are suitable for housing such projects. If you can get housing with an integral battery holder, you find it will make neat work of housing the project.
House the cells in a way that they are shaded and well protected from the sun. Take note that If the cells get overheated, their electrolyte leaks. That will damage the cell and making a mess.