This problem happens on Revision C regulator boards. It does not happen in earlier versions. To increase efficiency and to prevent reverse flow and deep discharge of the battery, we changed the board to improve the variance of the charging voltage as a function of temperature for maximum efficiency. To do this, ground the lug on the Rev. C board. The weather station must also be grounded. To ground the weather station, do the following. If you have a Weather Monitor II or a Weather Wizard III with a Protected Junction Box, ground the ground terminal (JP2) on the Protected Junction Box. If you do not have a Protected Junction Box, ground the station by running a wire to ground from the "Black" wire P1 terminal on the regulator board. NOTE: If you want to "Float" the station (no ground at all), connect the solar panel to the station using a jumper between the ground terminal on the regulator board and the "Black" wire P1 terminal on the regulator board.