Battery charger having temperature compensated charge rate

A battery charging circuit is disclosed which rapidly charges a battery from some level of discharge, including fully discharged, to fully charged without endangering the battery. The charging circuit includes a control circuit which provides switching type regulation responsive to current, voltage and temperature signals from the battery, and also a timer circuit for automatically halting the charging current to a defective battery. The control circuit receives a temperature compensated voltage signal (TCVS) which is useful for effectively implementing a charging program which includes a low constant current mode, a high constant current mode, and a constant voltage mode. The TCVS is generated by connecting a thermistor responsive to battery temperature in parallel with one resistor of a resistive voltage divider network which is connected across the battery terminals. The output of the thus modified voltage divider network when plotted against temperature is a nonlinear curve which, with proper selection of ohmic values for the resistors and thermistor, corresponds to a temperature/voltage relationship for the battery which is known from experimental results to be effective for charging the battery.