A compact battery booster comprising: an internal battery to supply a starting current to jump start an engine operably coupled with an external battery ; a processor operatively coupled with a reverse polarity sensor configured to detect a polarity of the external battery , a temperature sensor configured to detect a temperature of said internal battery , and a voltage sensor configured to detect a voltage of said internal battery ; a display device operatively coupled to the processor , the display device configured to display a state of charge of said internal battery ; a direct current DC output port to supply the starting current, wherein the DC output port is configured to electrically couple with a set of conductors configured to supply power to the external battery or the engine; and a power management circuit operatively coupled to the processor and the internal battery , the power management circuit to selectively provide the starting current to the external battery or the engine via the DC output port , wherein the power management circuit is configured to supply the starting current via the DC output port if the polarity of the external battery is not reversed, the temperature of said internal battery is within a predetermined temperature range, and the voltage of said internal battery meets or exceeds a predetermined voltage; characterized by the internal battery being an internal lithium ion battery , wherein the internal lithium ion battery is rated at least 3,000 mAh and the starting current is at least 200 amperes a universal serial bus USB port to supply a first current; a voltage converter to receive an input voltage and to output a predetermined charge voltage to said internal lithium ion battery ; and a supercapacitor , wherein said power management circuit is also operatively coupled to the supercapacitor and wherein the internal lithium ion battery can supply sufficient current to overcome the effects of the depleted external battery , while the supercapacitor may supply a peak current. wherein the voltage converter is a single-ended primary-inductor converter and the input voltage is a variable input voltage between 5 volts DC and 20 volts DC, wherein the single-ended primary-inductor converter is adapted to draw current from the depleted external battery for charging the supercapacitor , and wherein the processor in conjunction with a supercapacitor controller is adapted to prevent the supercapacitor in combination with a lithium battery from discharging the current back to the depleted external battery until the engine is started. an internal battery to supply a starting current to jump start an engine operably coupled with an external battery ; a processor operatively coupled with a reverse polarity sensor configured to detect a polarity of the external battery , a temperature sensor configured to detect a temperature of said internal battery , and a voltage sensor configured to detect a voltage of said internal battery ; a display device operatively coupled to the processor , the display device configured to display a state of charge of said internal battery ; a direct current DC output port to supply the starting current, wherein the DC output port is configured to electrically couple with a set of conductors configured to supply power to the external battery or the engine; and a power management circuit operatively coupled to the processor and the internal battery , the power management circuit to selectively provide the starting current to the external battery or the engine via the DC output port , <EOS>