A portable charger may have an indicator to check if the battery is fully charged. Otherwise, you can also take note of a simple formula for the average charge time, which is the ratio of the amp/hour rating versus charger rating in amperes. Allocate an additional 10% as an allowance for optimum charge.
Most portable solar chargers can absorb energy from the sun directly. During these days the portable wind turbines are also purchased by the peoples. Moreover, some of them include the Kinesis K3, which can work very efficiently. There are some examples of solar chargers which includes the models which are designed to be placed on the control panel of an automobile and are usually plugged into the cigar lighter, just to keep the battery topped up. Many portable solar charge are smaller in size, which are designed to charge a range of varies cell phones, mobile phones, iPods and many other portable audio equipments.