This is an upgrade of an earlier single battery unit. When my cell phone goes low and I am without my charger, as when my car breaks down and is towed to repair shop and I am in a rental car, it is great to have the capacity to quickly add charge to the phone. Toss one in the glove box for that, 'Just in case' moment. The dual battery unit charged my Smart Phone to about 50% (from dead) in 15 minutes.