How do you connect two 12 volt batteries into a 24 volt hitachi ex60 excavator?

Connect the two 12 volts batteries in Series. Battery 1 & 2. Connect the negative post (-) of battery 1 to the negative (-) ground cable. Then connect the positive (+) post of battery 1 to the negative (-) post of battery 2. Connect the positive (+) post of battery 2 to the positive (+) cable. You now have 24 volts as the batteries are wired in series.