A solar battery charger is a device that uses a bank of solar cells to generate a trickle charge for recharging batteries. Solar chargers need no power outlet, only the free energy available from the Sun during daylight hours. Their only disadvantage is that they work more slowly than plug-in types and may take a day or more to charge up a set of batteries. For this reason, it's a good idea to have an extra set of batteries, so that one set can be charged while the other is in use.

There are now a huge number of solar battery chargers, intended for a variety of purposes, on the market. Some, such as the one illustrated here, are designed to recharge the batteries of small electronic devices such as mobile phones and mp3 players. Others will charge 12V batteries for use in cars and boats.