Anyone using Portable Media Players (PMPs) in a remote location knows the challenges of charging batteries. The easiest way to store energy for a PMP is with a battery charger that plugs into an AC wall outlet connected to the power grid (mains). However, in remote locations solar panels or human powered generators must be used. Anyone who has used a photovoltaic panel or a hand cranked generator knows that these methods of charging batteries are much more difficult compared to AC battery charger. Some projects are using very large solar panels (9 square feet) while others spend a great deal of time cranking.

When using PMPs in these remote locations every lumen and decibel counts. Some Portable Media Players (PMPs) only play audio, while others include video. Audio (sound) output is measured in decibels (volume). The louder the audio the greater the drain on the battery. Proper adjustment of the volume of an audio PMP preserves battery energy. However, if the volume is too low, some of the listeners may not hear well and will not be learning as much from the audio lessons. Two loudspeakers with the volume set to medium placed on both ends of a class of 80 listeners will consume less energy compared to one loudspeaker set at maximum volume. Two speakers will allow for more students achieving greater comprehension as listeners.

Video output can be measured in lumens (brightness). The larger or the brighter the video display, the greater the drain on the battery. When PMPs with large displays are used for audio lessons, battery energy is consumed unessesarily. When video clips are played on PMPs with a small screen and too many viewers are trying to watch the video, some students will not be learning as much from the video lessons. In this case a PMP with a larger display will allow more students to achieve greater comprehension as viewers. If a particular lesson is not greatly enhanced by the addition of video clips, then perhaps the lesson should be presented only with audio. Video should not be used simply because it can be used.

Lumen and decibels consume battery energy which can be measured in milliamperes or milliamps (mA). When measured over time this can be expressed in milliamp hour (mAh). PMPs with a large video display consume far more milliamps compared to a small PMP playing audio file with a small dot matrix displaying the name of the file.

Electricity (measured in milliamps) is captured by solar panels and stored in batteries. On a cloudless day, the sun shines at 95,000 lumens. This is converted into electricity, stored in batteries and then drained in the conversion to light (lumens) to play a video on a PMP.

People working with PMPs in remote locations know that every square inch of a solar panel is costly and every hour of sun is precious during rainy days. People working with PMPs in remote locations also know that every turn of a hand crank or push of a foot pedal seems to contribute far less to charging batteries than we initially imagined before we started cranking.

Make every lumen and every decibel count. Don't squander these tiny learning resources, yet be sure that every student gets enough of them in order to comprehend that which is being taught.

A one hour audio file is about 14 megabytes (MB) One Gigabyte (GB) can store about 70 hours of voice files.