Auxiliary battery charge control circuit

A circuit for charging and discharging an auxiliary battery and for disconnecting said auxiliary battery from a main battery, comprising:

• an auxiliary battery and a main battery connected in parallel to a load device;
• a series connected diode and resistor connected between said auxiliary battery and said main battery for charging said auxiliary battery from said main battery during times in which a voltage upon said main battery exceeds by a threshold amount a voltage upon said auxiliary battery;
• an auxiliary battery charge control circuit connected between said main battery and said auxiliary battery for disconnecting said auxiliary battery from said main battery during times in which a voltage upon said main battery exceeds a threshold mount above the voltage upon said auxiliary battery and is less than a threshold mount above a ground potential;
• said auxiliary battery charge control circuit comprises:
• a first and a second voltage divider coupled in parallel between said ground potential and said main battery;
• a first and a second comparator having a mutually coupled output, said first comparator includes an inverting input adapted to receive a first divided voltage from said first voltage divider and said second comparator includes a non-inverting input adapted to receive a second divided voltage from said second voltage divider, wherein said first divided voltage is less than said second divided voltage;
• a switch transistor having a switch transistor base and a switch transistor conductive path, said switch transistor base is connected to said mutually coupled comparator output and said switch transistor conductive path is modulated by said switch transistor base and is connected between a current limiting resistor and said ground potential;
• and
• a battery connect transistor having a battery connect transistor base and a battery connect conductive path, said battery connect transistor base is connected through said current limiting resistor to said switch transistor conductive path, and wherein said battery connect conductive path is connected between said auxiliary battery and said main battery, whereby changes in conductivity of said switch transistor conductive path correspondingly cause changes in connectivity between said auxiliary battery and said main battery.