Accordiing to a new researc by the NASA's Lunar Science Institute, Lunar craters may be charged with a >100.000V by the Solar wind.

The electrical effect is due to the solar wind, which contains a large number of ions. When the solar wind is trapped in the lunar craters, their electrical charge is trapped with them.

This results in a potential difference from crater-bottom to the top of the crater walls. This creates a potential difference, which can be translated to a low-amp electrical power. The phenomena is comparable to electrially charged wheathher conditions during a thunderstorm here on earth, which has a high voltage, but a low amplitude

The  paper on this research published March 24 in the Journal of Geophysical Research

Sources: NASA and physorg