Features. Charges all standard 61224 volt maintenance-free batteries with 4 charging positions. 120 minute automatic timer.. Fully portable. Heavy duty vacuum impregnated transformer to seal the unit from external agents.. Multi-diode rectifiers to take over in case of failure.. Fan cooling mechanism prevents overheating improving the units life significantly.. Precautions against incorrect polarity with patented StopGo-light technology.. 500 amp clamps are covered with vinyl insulation will not arc or spark.. Heavy duty chrome plated handle.