Apparatus to prevent complete battery discharge

An apparatus for preventing complete discharge of a battery electrically connected in series with a load, said apparatus comprising:

• current detector means, connected in series with the battery, for detecting a battery current flowing through the battery;
• voltage detector means, connected in parallel with the battery, for detecting a battery voltage of the battery;
• temperature detector means for detecting a battery temperature of the battery;
• switching means, connected between the load and the battery, for selectively closing and opening an electrical connection between the load and the battery;
• and,
• computation means for controlling said switching means in accordance with the battery current detected by said current detector means, the battery voltage detected by said voltage detector means and the battery temperature detected by said temperature detector means;
• wherein said computation means includes
• (a) battery state detecting means for generating a reference voltage having a voltage level dependent on the battery current detected by said current detector means and the battery temperature detected by said temperature detector means, said battery state detecting means being responsive to said current detector means to decrease the reference voltage when the battery current increases and to increase the reference voltage when the battery current decreases, and being responsive to said temperature detector means to increase the reference voltage when the battery temperature increases and to decrease the reference voltage when the battery current decreases, and
• (b) comparator means for comparing the reference voltage generated by said battery state detecting means with the battery voltage detected by said voltage detector means, and for generating a first output signal when the battery voltage detected by said voltage detector means becomes less than the reference voltage generated by said battery state detecting means, wherein said switching means is responsive to said first output signal to open the electrical connection between the load and the battery.