A compact battery charger for charging a battery comprising: a microprocessor; a set of terminals operatively coupled to said microprocessor and configured to electrically couple with an automotive battery; and an internal lithium ion battery, wherein the internal lithium ion battery is a lithium ion battery, wherein a single-ended primary-inductor converter may be configured to receive an input voltage of 5 VDC to 20 VDC and output a predetermined DC charge voltage to said internal lithium ion battery.