This 3.7V USB charger will charge your battery to a fully charged state of 4.2V. You can use your computer, TV, Surge protector, or a USB wall adapter (not included) to charge your REBEL battery. Don't use anything with a higher output than 5V 2A (2000mA). The Red charging light should take about 1.5 hrs to go out, indicating a full charge, from a diminished state. Shorter if it is the first charge out of the box. Please make sure that you never charge a battery unattended, and never charge a battery on a flammable surface. Don't charge more than 2 hrs, if the charging light hasn't gone out, something is wrong.