It depends on what you mean by “dead”. If the battery is flat because you left the headlights or stereo on, or you haven’t driven the car for ages... then yes you can. However, if the battery fails internally it cannot be recharged. If you have a smart battery charger, it should let you know if the battery is faulty. For example, the REDARC SmartCharge battery charger has a flashing warning triangle to indicate battery failure.