Lithium battery automatically jumps to charge when fully charged
This Jump Starter has an excellent internal lithium-ion battery. I used it to start my motorcycle with a dead battery. With 1600 Amp storage "jump" power, It took about 3 hours to fully charge from out of the box. I opened it and it had about ½ charge. The USB charging with a 2a charger took less than 3 hours. It is very convenient.