NOVELTY - The product comprises battery cells or modules, relays arranged to charge the battery cells or modules in parallel and discharge the battery cells or modules in series, a temperature actuated switch connected to a sensor on the outer surface of the battery modules or cells, a zener or avalanche diode connected to two poles of the battery modules or cells with the low-voltage polarity of the diode opposite to the polarity of the cell, and a diode or voltage activated switch connected to two poles of the cells. The switch is constructed and arranged to bypass the cell.    USE - The product such as photovoltaic system comprising battery cells or modules is useful in a lithium ion battery system for determining the maximum power point voltage of the photovoltaic solar cells and the optimum charge voltage of the lithium ion battery cells (claimed), for storing and recovering renewable solar energy in batteries, and in extended-range electric vehicles such as the Chevy volt and plug-in hybrid vehicles.    ADVANTAGE - The product such as photovoltaic system comprising battery cells or modules avoids overcharging, heat generation, cell damage and safety risks when the cell strings and battery modules are combined and charged in battery packs, has improved lifetimes, and prevents polarity reversal i.e. flipping of any battery cell in a series string due to excessive discharging of a cell.    DETAILED DESCRIPTION - The product comprises battery cells or modules, relays arranged to charge the battery cells or modules in parallel and discharge the battery cells or modules in series, a temperature actuated switch connected to a sensor on the outer surface of the battery modules or cells, a zener or avalanche diode connected to two poles of the battery modules or cells with the low-voltage polarity of the diode opposite to the polarity of the cell, and a diode or voltage activated switch connected to two poles of the cells. The switch is constructed and arranged to bypass the cell by disconnecting the cell from adjacent cells to allow the temperature of the cell to exceed a predetermined value. Whenever the voltage drop across the cell falls below a set voltage, the diode or switch bypasses the cell by disconnecting the cell from adjacent cells. A charge actuated switch is connected to the poles of the battery modules or cells and arranged to bypass the battery module or cell by disconnecting the same from adjacent battery modules or cells when a set discharge has occurred equal to a predetermined percentage of the full charge for the battery module or cell. A bypass diode is connected to the poles of the battery modules or cells. Whenever the biased voltage drop across any cell falls to zero during the process of discharging the battery modules or cells, the bypass diode automatically carries the current flowing from other cells around the effected cells to prevent polarity reversal of the effected cell in which the current flows in the wrong direction. The photovoltaic system connects a specific number of solar cells in series with the lithium ion cells in series so that under operating conditions, the maximum power point voltage of the photovoltaic system matches or is slightly less than the overall optimum charging voltage of the lithium ion battery module.    DESCRIPTION OF DRAWING(S) - The figure shows a simplified view of solar battery charger using multiple pole double throw relays for contactors to allow charging of battery cells and modules in parallel and discharging them in series.