This almost trivial circuit may be used to charge a pair of AA or AAA sized rechargeable battery cells from sunlight. The circuit has been used to keep a Palm Pilot and walkman radio running perpetually. This is an unregulated charger, proper charging is achieved by placing the unit in the sun for a known amount of time, this time varies according to the battery type.
Each of the solar cells develops about 0.5 volts across itself when in full sunlight. The string of 8 solar cells puts out around 4V with no load. When the solar cells are connected to a battery, a current will flow and the battery will charge.